Lake Baikal

This lake is situated in the south of the Russian region of Siberia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast, it is the most voluminous freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water.
Lake Baikal is the deepest and  the clearest of all lakes in the world.
Lake Baikal was known as the "North Sea" in historical Chinese texts. It was situated in the then Xiongnu territory that stretched from the empire of the Han Dynasty in the south, to the Siberian taiga north of the lake, and saw military excursions led by the army of the Han Dynasty engaging the Xiongnu during the Han-Hun Wars.Only a few information was known to Europeans about the lake until Russia expanded into the area in the 17th century. The first Russian explorer to reach Lake Baikal was Kurbat Ivanov in 1643.