A volcano in Antarctica called Erebus is home to a network of ice caves. Hot gasses from the volcano carves through the thick ice to leave channels where ice crystals then grow. Dr. Kayla Iacovino wrote about visiting one of them called Warren Cave, and included more photographs. http://www.sciencefriday.com/blog/2010/12/the-ice-caves-of-mt-erebus-antarctica/ -via The Dystenium Science Daily
Previously: Ice Fumarole in Antarctica