In 1991, Doris Manner contended that the mythical city of Vineta (sometimes Wineta) in the Baltic Sea was linked to Atlantis.
The myth of Vineta evolved around the tradition about the medieval emporium called Jumne, Jomsborg (with which Vineta is sometimes identified), Julin or similar names by the chronicles. There are several Vineta myths, all of them having in common an excessive, voluptuous or blasphemous way of life of the Vinetans who were then punished by a flood which took the city to the bottom of the Baltic. In some variants of the myth, the city or parts thereof reappear on certain days or can be seen from a boat, making the warning transported by the myth more tangible for the audience. Some variants of the myth have Vineta sunken off Koserow (on the isle of Usedom). Several maps published between 1633 and 1700 have the sunken "Wineta" east of the island of Ruden northwest of Usedom.
Rudolf Virchow said: "Vineta is Wollin!" Based on the primary sources outlined above, Adolf Hofmeister (de) in 1931/32 formulated the thesis that Vineta, Jumne, Julin, Jomsborg etc. are all different spellings used for the same place on the site of today's town of Wolin. Beginning in the 1930s, and continued after the annexation of Wolin to Poland after World War II, archaeologists unearthed the remains of a large settlement there. Hofmeister's thesis is the only mainstream thesis regarding the location of Vineta in today's historiography.
Curiously, in 2011, the Baltic Sea anomaly was discovered. It is a 60-meter (200 ft) circular rock-like formation on the floor of the Baltic Sea, discovered by Peter Lindberg, Dennis Åsberg and their Swedish "Ocean X" diving team. The team reported that the formation rests on a pillar and includes a structure similar in appearance to a staircase, leading to a dark hole.
Commentators have suggested that the structure could be a World War II anti-submarine device, a battleship gun turret, sediment dropped by a fishing trawler, or a flying saucer. Several experts have stated that it is most likely a natural geological formation.
The Baltic Sea is located between Central and Northern Europe, from 53°N to 66°N latitude and from 10°E to 30°E longitude. It is bounded by the Swedish part of the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and the Little Belt. The Kattegat continues through Skagerrak into the North Sea and the Atlantic Ocean. The Baltic Sea is connected by artificial waterways to the White Sea via the White Sea Canal, and to the German Bight of the North Sea via the Kiel Canal. The central part, also called the Baltic Proper, is bordered on its northern edge by the Gulf of Bothnia, on its northeastern edge by the Gulf of Finland, and on its eastern edge by the Gulf of Riga.
While Tacitus called it Mare Suebicum after the Germanic people called the Suebi, the first to name it the Baltic Sea (Mare Balticum) was the eleventh-century German chronicler Adam of Bremen.
The origin of the latter name is speculative. It might be connected to the Germanic word belt, a name used for two of the Danish straits, the Belts, while others claim it to be derived from Latin balteus (belt). Adam of Bremen himself compared the sea with a belt, stating that it is so named because it stretches through the land as a belt (Balticus, eo quod in modum baltei longo tractu per Scithicas regiones tendatur usque in Greciam). He might also have been influenced by the name of a legendary island mentioned in the Natural History of Pliny the Elder. Pliny mentions an island named Baltia (or Balcia) with reference to accounts of Pytheas and Xenophon. It is possible that Pliny refers to an island named Basilia ("kingdom" or "royal") in On the Ocean by Pytheas. Baltia also might be derived from "belt" and mean "near belt of sea (strait)". Meanwhile others have concluded that the name of the island originates from the Indo-European root *bhel meaning white, fair. This root and its basic meaning were retained in both Lithuanian (as baltas) and Latvian (as balts). On this basis, a related hypothesis holds that the name originated from this Indo-European root via a Baltic language such as Lithuanian.
Another explanation is that, while derived from the aforementioned root, the name of the sea is related to names for various forms of water and related substances in several European languages, that might have been originally associated with colors found in swamps. Yet another explanation is that the name originally meant "enclosed sea, bay" as opposed to open sea. Some Swedish historians believe the name derives from the god Balder of Nordic mythology.
In the Middle Ages the sea was known by variety of names. The name Baltic Sea became dominant only after 1600. Usage of Baltic and similar terms to denote the region east of the sea started only in 19th century.
The Baltic Sea is one of the largest brackish inland seas by area. The Baltic Sea occupies a basin formed by glacial erosion during the last few ice ages.
The Baltic Sea is about 1,600 km (1,000 mi) long, an average of 193 km (120 mi) wide, and an average of 55 m (180 ft, 30 fathoms) deep. The maximum depth is 459 m (1506 ft) which is on the Swedish side of the center. The surface area is about 349,644 km²  (145,522 sq mi) and the volume is about 20,000 km³ (5040 cubic miles). The periphery amounts to about 8,000 km (5,000 mi) of coastline.
The Baltic Sea's salinity is much lower than that of ocean water as a result of abundant freshwater runoff from the surrounding land, combined with the shallowness of the sea itself.
The Baltic Sea, with its unique brackish water, is a result of meltwater from the Weichsel glaciation combining with saltwater from the North Sea when the straits between Sweden and Denmark opened. Initially, when the ice began melting about 10,300 BP, seawater filled the isostatically depressed area, a temporary marine incursion that geologists dub the Yoldia Sea. Then, as post-glacial isostatic rebound lifted the region about 9500 BP, the deepest basin of the Baltic became a freshwater lake, in palaeological contexts referred to as Ancylus Lake, which is identifiable in the freshwater fauna found in sediment cores. The lake was filled by glacial runoff, but as worldwide sea level continued rising, saltwater again breached the sill about 8000 BP, forming a marine Littorina Sea which was followed by another freshwater phase before the present brackish marine system was established. "At its present state of development, the marine life of the Baltic Sea is less than about 4000 years old," Drs. Thulin and Andrushaitis remarked when reviewing these sequences in 2003.