Satellite images have revealed a strange hole in Antarctica.
After scientists ruled out whirlpools and sinkholes, they have been forced to look back in time to find the answer.
See also: Mysterious pyramids found in Antarctica
See also: Mysterious floating island appears in Argentina
In the geological past, Antarctica had a different climate, and some experts believe that lakes have been trapped there for millions of years.
These ancient subterranean bodies of water are known as ghost lakes. What on Earth is investigating.