A liquid lake the size of Lake Ontario sits sealed under 4km of Antarctic ice

Lake Vostok, buried beneath roughly 4 km of ice near Russia's Vostok Station, is the largest of more than 400 known subglacial lakes in Antarctica, kept liquid by geothermal heat and the insulating weight of ice above it. Russian scientists finally drilled through to its surface in 2012, after decades of exploration, raising hopes of finding microbial life isolated from the rest of the planet for over a million years.

— Scientific and geological record, Lake Vostok — Subglacial lake, East Antarctica; drilled 2012