See the LAKE BAIKAL, Russia

The deepest lake in the world
One of the world’s natural wonders, Lake Baikal is an immense, crescent-shaped chasm in the earth, nearly 640km long and up to 80km wide. Situated in Russia's great Siberian wilderness, its record-breaking size is matched only by its remoteness; the lake is roughly 3,200km west of the Pacific Ocean, 5,100km east of Moscow and 200km north of the Mongolian border.

Plunging downwards for more than a kilometre, Baikal is the deepest lake in the world, holding about 23,000 cubic kilometres of water – more than the five North American Great Lakes combined. More than 300 rivers flow into Lake Baikal, but only one – the Angara – flows out, eventually draining into the Arctic Ocean far to the north. Geological activity means the lake’s floor keeps dropping a little each year, and the water is so clear in places that you can often see objects 40m below the surface.
Source: bbc.com