Lake Baikal

This massive lake in southern Siberia is the world's largest freshwater lake, containing 23% of the world's fresh surface water, the world's deepest lake, and the world's oldest, at 25–30 million years. It is slightly larger than Belgium and is among the world's clearest lakes. It has an immensely rich biodiversity of flora and fauna, and its vastly contrasting ice and summer seasons provides its millions of annual visitors a uniquely different experience, and is often accessed via the Trans-Siberian Railway.