Lake Baikal

The deepest lake in the world at 1,642 metres, the oldest at 25 to 30 million years, and the largest by volume: 23,615 cubic kilometres, somewhere between 22 and 23 percent of all the fresh surface water on the planet and about 19 percent of the unfrozen fresh water. Its surface is 31,722 square kilometres, slightly bigger than Belgium. Isolation for that long has produced its own world, over 1,000 plant and 2,500 animal species with a great many found nowhere else, including the nerpa, the Baikal seal, the only seal that lives entirely in fresh water. From early January to May or June the whole thing freezes over, half a metre to a metre and a half thick, clear enough in places to look straight down into it. UNESCO World Heritage since 1996. Southern Siberia.