A photo of Lake Baikal, in Siberia, the world’s deepest, and largest, freshwater lake, taken by Chris Hadfield, currently a flight engineer on the International Space Station (ISS).
Holding almost a fifth of the world’s unfrozen surface fresh water, Lake Baikal is also said to be the clearest, and oldest, lake on Earth.
See a larger version here. Flick through Hadfield’s Twitter page for more of his stunning in-Earth-orbit photography.