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Walchensee or Lake Walchen is one of the deepest and largest alpine lakes in
Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...
, with a maximum depth of and an area of . The lake is south of
Munich Munich is the capital and most populous city of Bavaria, Germany. As of 30 November 2024, its population was 1,604,384, making it the third-largest city in Germany after Berlin and Hamburg. Munich is the largest city in Germany that is no ...
in the middle of the Bavarian
Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...
. The entire lake, including the island of Sassau, is within the municipality of Kochel. The lake and island are owned by the Bavarian State. To the east and the south, the lake borders the municipality of Jachenau.


Etymology

The name ''Walchen'' comes from
Middle High German Middle High German (MHG; or ; , shortened as ''Mhdt.'' or ''Mhd.'') is the term for the form of High German, High German language, German spoken in the High Middle Ages. It is conventionally dated between 1050 and 1350, developing from Old High ...
and means "strangers". All Roman and romanized peoples of the Alps south of Bavaria were known to the locals as ''Welsche'' or even ''Walche''. This is also true of the etymology of the
Swiss Swiss most commonly refers to: * the adjectival form of Switzerland * Swiss people Swiss may also refer to: Places * Swiss, Missouri * Swiss, North Carolina * Swiss, West Virginia * Swiss, Wisconsin Other uses * Swiss Café, an old café located ...
Lake Walen and the
Salzburg Salzburg is the List of cities and towns in Austria, fourth-largest city in Austria. In 2020 its population was 156,852. The city lies on the Salzach, Salzach River, near the border with Germany and at the foot of the Austrian Alps, Alps moun ...
Wallersee. Another possible interpretation is that it comes from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''Lacus vallensis'', meaning "lake in a valley". On 16th-century maps, the lake is also labelled ''dicto Italico'', meaning "leading to Italy", probably because the route through the Walchensee valley led through Mittenwald and
Innsbruck Innsbruck (; ) is the capital of Tyrol (federal state), Tyrol and the List of cities and towns in Austria, fifth-largest city in Austria. On the Inn (river), River Inn, at its junction with the Wipptal, Wipp Valley, which provides access to the ...
to Italy.


Geography


Genesis

Walchensee fills a tectonic valley, part of the ''Bayerisches Synklinorium'' (Bavarian
Syncline In structural geology, a syncline is a fold with younger layers closer to the center of the structure, whereas an anticline is the inverse of a syncline. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed ...
) and from rocks of the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
period (the main dolomite, Plattenkalke, and Kössener layers). The extreme depth of the lake, , is the result of this tectonic formation. The rock faces of the northwestern shore clearly show the steep arrangement of the rock layers. The creation of the lake from the forces of mountain building indicate that Walchensee could be one of the oldest lakes in Germany. During the
ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages, and g ...
, the Isar–Loisach glacier repeatedly left its mark on the morphology of the area and thereby the Walchensee.


Location and surrounding communities

The lake has a shoreline of approximately and contains of water. The Jachen is the natural outflow of the lake, eastwards through the valley of Jachenau to the
Isar The Isar () is a river in Austria and in Bavaria, Germany. Its source is in the Karwendel mountain range of the Alps. The Isar river enters Germany near Mittenwald and flows through Krün, Wallgau, Bad Tölz, Munich, and Landshut before reaching ...
. Obernach is the largest natural inflow to the lake, entering from the southwest. Together with the artificial inflow (see "Peculiarities"), the lake has a catchment basin of . Walchensee lies at above sea level. It is surrounded by wooded mountains. To the northwest stands the HerzogstandHeimgarten group at and respectively and to the west is the valley of the Eschenlaine. The south side of the Eschenlaine valley is the Simetsberg (), which is the end of the Ester Mountains. To the south of the lake, the Altlacher Hochkopf separates Walchensee from the valley of the Isar. On the eastern shore lies the Jachenau, a long alpine valley that stretches in the direction of Lenggries. The northeast is dominated by the Benediktenwand. A little further to the west is Jochberg (), which completes the valley wall. Between Herzogstand and Jochberg is little Kesselberg, which because of its relatively low prominence appears as a depression between the two higher peaks, but actually separates Walchensee from Kochelsee, below. Directly on the west bank of the lake is the tiny ''Luftkurort'' settlement of Walchensee, with only about 600 inhabitants. Walchensee belongs to the municipality of Kochel as do the yet smaller settlements of Urfeld at the northern tip of the lake, Zwergen on the western shore, and the houses of Einsiedl am Walchensee on the
orographic Orography is the study of the topographic relief of mountains, and can more broadly include hills, and any part of a region's elevated terrain. Orography (also known as ''oreography'', ''orology,'' or ''oreology'') falls within the broader disc ...
left bank of the Obernach at the far southwestern end of the lake. The houses of Einsiedl am Walchensee on the right bank of the Obernach and Altlach on the southern shore, the farmsteads of Matheis, Christopher, and Breitort, Sachenbach on the east shore, and Niedernach in the far southwest, belong to the municipality of Jachenau. Between the settlements of Walchensee and Einsiedl, the Katzenkopf peninsula reaches into the lake. The settlement of Zwergen lies on this peninsula. The surface of the lake forms a north-facing triangle, with the southern shore forming a base from Einsiedl to Niedernach and the height reaching from Breitort to Urfeld.


Climate

Due to its location in a valley, the lake is protected from northern and eastern winds. The relatively low mountains on the south shore let in the optimal amount of sunlight, giving Walchensee a milder climate than one might expect in the mountains. During the summer months, heat on southern side of Herzogstand and Jochberg create strong
thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
s on sunny days. Stable thermal winds blow generally southwest. When the thermals carry saturated air masses from the Walchensee high into the air and mix with air from the more northerly Kochelsee by a prevailing wind from the northwest, it can lead to particularly violent thunderstorms. In contrast to a foehn, when a
katabatic wind A katabatic wind (named ) is a downslope wind caused by the flow of an elevated, high-density air mass into a lower-density air mass below under the force of gravity. The spelling catabatic is also used. Since air density is strongly dependent o ...
blows from south to north, the associated dry air ensures excellent visibility.


History

Since prehistoric times the local population has felt a close association with the lake; for example until the 18th century it was customary to throw consecrated gold coins into the deepest part of the lake. The wealth of fish in the lake led the monasteries of Benediktbeuern Abbey and Schlehdorf Abbey to claim Walchensee by 740 AD. The monasteries owned the lake until
secularization In sociology, secularization () is a multilayered concept that generally denotes "a transition from a religious to a more worldly level." There are many types of secularization and most do not lead to atheism or irreligion, nor are they automatica ...
in 1803. The abbey at Benediktbeuern had more rights than Schlehdorf. Today the free state of
Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...
owns Walchensee. In Munich around 1900, the idea of using the drop between Walchensee and Kochelsee to generate power was born. Dives to survey the lake bottom were already under way by 1903. The driving force behind this venture was Oskar von Miller, who founded the
Deutsches Museum The Deutsches Museum (''German Museum'', officially (English: ''German Museum of Masterpieces of Science and Technology'')) in Munich, Germany, is the world's largest museum of science museum, science and technology museum, technology, with a ...
in 1903. The approval process dragged on until 1918. Construction work began immediately after
World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
. On 24 January 1924 water from Walchensee turned the turbines at the Walchensee Hydroelectric Power Station on the shore of the Kochelsee for the first time. During
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
at least two aircraft ditched and sank into the lake. On 3 October 1943, an
Avro Lancaster The Avro Lancaster, commonly known as the Lancaster Bomber, is a British World War II, Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to ...
from the
Royal Air Force The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
crashed here. In April 1945 the
Wehrmacht The ''Wehrmacht'' (, ) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the German Army (1935–1945), ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmac ...
and officials of the
Reichsbank The ''Reichsbank'' (; ) was the central bank of the German Empire from 1876 until the end of Nazi Germany in 1945. Background The monetary institutions in Germany had been unsuited for its economic development for several decades before unifica ...
approved a plan to store at least part of the reserves of the German Reichsbank at Einsiedl, a small hamlet on the south-west shore. Subsequently, the assets were buried in an undisclosed location in the crags above the Obernach power-plant. The assets consisted of 365 sacks, each with two
gold bar A gold bar, also known as gold bullion or a gold ingot, is a quantity of refined metallic gold that can be shaped in various forms, produced under standardized conditions of manufacture, labeling, and record-keeping. Larger varieties of gold ...
s, nine envelopes with gold documents, four crates of gold, two bags of gold coins, six boxes of Danish coins, and 94 sacks of foreign currency. The foreign currency was mainly
U.S. dollars The United States dollar (symbol: $; currency code: USD) is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it int ...
and
Swiss francs The Swiss franc, or simply the franc, is the currency and legal tender of Switzerland and Liechtenstein. It is also legal tender in the Italian exclave of Campione d'Italia which is surrounded by Swiss territory. The Swiss National Bank (SNB) i ...
. On 6 June 1945, the treasure was handed over to the
Allies An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not an explicit agreement has been worked out among them. Members of an alliance are calle ...
. One hundred gold bars and all the U.S. dollars and Swiss francs were missing. Possibly there are other hoards, where valuables such as other
currencies A currency is a standardization of money in any form, in use or currency in circulation, circulation as a medium of exchange, for example banknotes and coins. A more general definition is that a currency is a ''system of money'' in common use wi ...
or
gemstones A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewelry or other adornments. Certain rocks (such as lapis lazuli, opal, a ...
were hidden. Even today, speculation continues about the existence and exact location of such caches. Since the 1950s, Walchensee has become a popular destination for day trips from Munich and other upper Bavarian cities as well as for tourists. The local population now lives primarily from tourism.


Biology


Ecology

The clear waters with an average visibility of 8–10 m owes its turquoise-green color to the relatively high proportion of
calcium carbonate Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
. The waters of Walchensee rate as
water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...
class 1 under the saprobic system. The temperature of the water is relatively low, which is typical for a mountain lake. In summer the water temperature ranges from to and from to in the spring and fall. The nutrient load on the originally
oligotroph An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates o ...
ic Walchensee has declined since the mid-1980s, due to improvements in sanitation in Mittenwald. The Walchensee including its shores is a Landschaftsschutzgebiet ''landscape protection area''. Of the south shore, are set aside for recreational purposes, such as bathing. The rest of the shore drops steeply for the most part. The western lakeshore is undeveloped, with a few exceptions. The island of Sassau () is a nature reserve and is off limits all year round. The island is long and wide in the west. In the east it is only half as wide. Its highest point is above the surface of the lake.


Flora and fauna

The first fish were introduced into the lake more than 500 years ago: whitefish ''
Coregonus ''Coregonus'' is a diverse genus of fish in the salmon family (Salmonidae). The ''Coregonus'' species are known as whitefishes. The genus contains at least 68 described extant taxa, but the true number of species is a matter of debate. The type ...
'' sp. were introduced from Kochelsee in 1480, followed by char from
Tegernsee Tegernsee () is a Town#Germany, town in the Miesbach (district), Miesbach district of Bavaria, Germany. It is located on the banks of Tegernsee (lake), Lake Tegernsee, which is 747 m (2,451 ft) AMSL, above sea level. A spa town, it is su ...
. The lake environment can be divided into three zones: shore, bottom, and open water. The following table lists the fish that can be found in these zones. :: More than 50% of the fish species that live here are threatened or at least endangered in Bavaria, including the wels catfish and '' Rutilus meidingerii''. The swan mussel is also on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
of endangered plant and animals. In 2003,
Upper Bavaria Upper Bavaria (, ; ) is one of the seven administrative regions of Bavaria, Germany. Geography Upper Bavaria is located in the southern portion of Bavaria, and is centered on the city of Munich, both state capital and seat of the district gove ...
began a project to restock Walchensee with European crayfish '' Astacus astacus''. For this purpose, 1900 crayfish were captured in
Eibsee Eibsee (" yew lake") is a lake in Bavaria, Germany, 9 km southwest of Garmisch-Partenkirchen and roughly 100 km southwest of Munich. It is above sea-level and its surface area is . It is at the northerly base of the Zugspitze ( above s ...
, west of Garmish-Partenkirchen. The lake and Sassau island offer excellent breeding opportunities for many bird species and a safe winter quarters or resting place for migrating birds. In addition to red-necked and black-necked grebes,
mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa. It has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Arge ...
s, and
Eurasian coot The Eurasian coot (''Fulica atra''), also known as the common coot, or Australian coot, is a member of the rail and crake bird family, the Rallidae. It is found in Europe, Asia, Australia, New Zealand and parts of North Africa. It has a slaty-bla ...
s,
common merganser The common merganser (North American) or goosander (Eurasian) (''Mergus merganser'') is a large sea duck of rivers and lakes in forested areas of Europe, Asia, and North America. The common merganser eats mainly fish. It nests in holes in trees ...
s and great northern divers are sometimes seen. '' Ranunculus fluitans'' and ''
Myriophyllum spicatum ''Myriophyllum spicatum'' (Eurasian watermilfoil or spiked water-milfoil) is a submerged perennial aquatic plant which grows in still or slow-moving water. Eurasian watermilfoil is native to Europe, Asia, and North Africa, but has a wide geograph ...
'' grow just below the surface near the shore and in the lake's inlets. Unicellular organisms both vegetable (
diatoms A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
and
green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...
) and animal (
water flea The Diplostraca or Cladocera, commonly known as water fleas, is a superorder of small, mostly freshwater crustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory. Over 1000 species have been recog ...
s, genus ''
Cyclops In Greek mythology and later Roman mythology, the Cyclopes ( ; , ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguished. In Hesiod's ''Th ...
'' ) occur in virtually all areas of the lake. Native ''
Phragmites ''Phragmites'' () is a genus of four species of large perennial plant, perennial reed (plant), reed Poaceae, grasses found in wetlands throughout temperate and tropical regions of the world. Taxonomy The World Checklist of Selected Plant Famili ...
'' and ''
Schoenoplectus ''Schoenoplectus'' (club-rush ld World species bulrush or tule ew World species is a genus of plants in the Cyperaceae, sedge family with a cosmopolitan distribution. Note that the name bulrush is also applied to species in the unrelated ...
'' grow near the shore and waterlilies ''
Nymphaea alba ''Nymphaea alba'', the white waterlily, European white water lily or white nenuphar , is an aquatic flowering plant in the family Nymphaeaceae. It is native to North Africa, temperate Asia, Europe and tropical Asia (Jammu and Kashmir). Since '' ...
'' and ''
Nuphar lutea ''Nuphar lutea'', the yellow water-lily, brandy-bottle, or spadderdock, is an aquatic plant of the family Nymphaeaceae, native to northern temperate and some subtropical regions of Europe, northwest Africa, and western Asia. This species was us ...
'' offer shelter for
grass snake The grass snake (''Natrix natrix''), sometimes called the ringed snake or water snake, is a Eurasian semi-aquatic non- venomous colubrid snake. It is often found near water and feeds almost exclusively on amphibians. Subspecies Many subspecie ...
s and other animals.


Tourism

Like other large lakes, such as
Tegernsee Tegernsee () is a Town#Germany, town in the Miesbach (district), Miesbach district of Bavaria, Germany. It is located on the banks of Tegernsee (lake), Lake Tegernsee, which is 747 m (2,451 ft) AMSL, above sea level. A spa town, it is su ...
, Walchensee plays a major role is tourism for the region. Enthusiasts of
windsurfing Windsurfing is a wind-propelled water sport that is a combination of sailing and surfing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the Californian aerospace and surf culture. Windsurfing gain ...
and
sailing Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' (sailing ship, sailboat, raft, Windsurfing, windsurfer, or Kitesurfing, kitesurfer), on ''ice'' (iceboat) or on ''land'' (Land sa ...
take advantage of the continuous thermal winds of the summer months. Creation of thermals is encouraged by winds from the East or North and by the relatively large day and night temperatures. The clear waters with visibility of up to and a whole series of car, boat, and even aircraft wrecks make the lake particularly interesting for scuba divers. In addition to the usual activities, such as swimming and hiking, those seeking recreation in the winter months can hike and cross country ski in the surrounding mountains. The ''Herzogstandbahn'', a
gondola lift A gondola lift is a means of cable transport and type of aerial lift which is supported and propelled by cables from above. It consists of a loop of steel wire rope that is strung between two stations, sometimes over intermediate suppo ...
, runs from Spring to Fall from Walchensee up the Fahrenberg. From there one can walk past the Herzogstandhaus to the top of the Herzogstand in 30–45 minutes.


Fishing

The lake is owned by the Bavarian State and is managed by the Genossenschaft oberbayerischer Berufsfischer & Teichwirte. Fishing permits are available.


Points of interest


Walchensee Power Station

In 1924, Bayernwerk AG put the Lake Walchen Power Plant into operation on the south shore of Kochelsee. Six pipes carry water from Walchensee 200 m down the mountain to the hydroelectric plant. In order to increase the amount of water available for the plant, a 7-km long tunnel was driven in the
Karwendel The Karwendel is the largest mountain range of the Northern Limestone Alps. It is located on the Austria–Germany border. The major part belongs to the Austrian federal state of Tyrol (state), Tyrol, while the adjacent area in the north is part ...
to tap the Rißbach and
Isar The Isar () is a river in Austria and in Bavaria, Germany. Its source is in the Karwendel mountain range of the Alps. The Isar river enters Germany near Mittenwald and flows through Krün, Wallgau, Bad Tölz, Munich, and Landshut before reaching ...
rivers, feeding Walchensee. Overall, Walchensee has an average volume of 1.3 billion cubic meters. Two smaller hydroelectric plants were built directly on Walchensee: one at the mouth of the Niedernach in the southeast and one on the Obernach in the southwest. Large amounts of water are only taken from lake during winter months so as not to disturb the tourist industry during the peak season. Because of the large fluctuations in water level during the winter, the lake no longer freezes. * Maximum water level 802 m above sea level * Nominal water level 801.5 m above sea level * Minimum water level 795 m above sea level The ice that does form in the individual bays is very thin and is off limits.


Wrecks

On the lakebottom is a series of wrecks, including three aircraft. From World War II there is a
Messerschmitt Bf 109 The Messerschmitt Bf 109 is a monoplane fighter aircraft that was designed and initially produced by the Nazi Germany, German aircraft manufacturer Messerschmitt#History, Bayerische Flugzeugwerke (BFW). Together with the Focke-Wulf Fw 190, the ...
and a British
Avro Lancaster The Avro Lancaster, commonly known as the Lancaster Bomber, is a British World War II, Second World War heavy bomber. It was designed and manufactured by Avro as a contemporary of the Handley Page Halifax, both bombers having been developed to ...
bomber. Among the debris the remains of an Aero Commander 680W was found. The high-wing twin-engine plane with the markings D-ID MON crashed into the lake on 27 December 1978 after its tail broke off. The plane crashed in shallow water and was immediately salvaged along with its crew. The wrecks of two cars near the shore, a
Volkswagen Beetle The Volkswagen Beetle, officially the Volkswagen Type 1, is a small family car produced by the German company Volkswagen from 1938 to 2003. One of the most iconic cars in automotive history, the Beetle is noted for its distinctive shape. Its pr ...
and a Ford, are also popular for divers to explore.


Landscape painting

In 1934, the painter
Lorenzo Quaglio the Younger Lorenzo Quaglio the Younger (19 December 1793, Munich – 15 March 1869) was a genre paintings, genre painter and lithographer, born in Munich in the Electorate of Bavaria to the long Italian people, Italian pedigree of Quaglios. Life Quaglio stud ...
immortalized Walchensee in an oil painting titled simply ''Der Walchensee''. The painting hangs today in the Munich City Museum. After World War I, the artist
Lovis Corinth Lovis Corinth (21 July 1858 – 17 July 1925) was a German artist and writer whose mature work as a painter and printmaker realized a synthesis of impressionism and expressionism. Corinth studied in Paris and Munich, joined the Berlin Secessio ...
bought a house in Urfeld. From 1919 until the end of his life in 1925, the
Impressionist Impressionism was a 19th-century art movement characterized by visible brush strokes, open Composition (visual arts), composition, emphasis on accurate depiction of light in its changing qualities (often accentuating the effects of the passage ...
spent his summer months along with his wife at the lake. His success as a landscape painter rests on the work he did with Walchensee as a subject. He did more than 60 of these paintings.


References


External links

* {{Authority control Bad Tölz-Wolfratshausen Lakes of Bavaria