Along the Lake Baikal. Steam locomotives (class 2-10-0) L-3634 and L-3653 with passenger tourist train on 102 kilometer of "Circum-Baikal Railway". The train goes few time a week from Irkutsk to Port Baikal and back. Lake Baikal is the largest (by volume) freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water. At 1,642 m (5,387 ft), Baikal is the world's deepest lake. It is considered among the world's clearest lakes and is considered the world's oldest lake — at 25 million years.