Lake Vostok lies about 4000 metres beneath the polar ice in Antarctica and was discovered by British and Russian glaciologists in 1998. It is directly beneath Russia's Vostok Station, hence the name. It is thought to be the fourth largest freshwater body in the world, at around 230 km long by 50 km wide, with a maximum water depth of over 500 metres. It is still liquid because the temperature below the ice sheet is temperate; being that far beneath the rest of Antarctica spares it from the continent's extreme cold.

Very little is known about the contents of the lake, but scientists have recently bored a hole through the ice to within 120m of the lake's water surface and have found pollen grains and inert micro-organisms. After having been cut off from the rest of the earth for over one million years, scientists, including those from NASA, are particularly interested in the contents of this exceptionally oligotropic ecosystem, as the conditions which exists within it closely resemble those thought to exist on the Europa, one of Jupiters moons.

Because of the intense weight bearing down from the ice sheet above, around 340 times atmospheric pressure, the water contains almost no dissolved oxygen, carbon dioxide, methane, or other gases, and there is little possibility of geothermal vents existing at the bottom of the lake to provide warmth, but it is thought that microbes exist within this inhospitable terrain.