Ice cave on the Kamchatka Peninsula of Russia. It was formed by a stream flowing from the hot springs associated with the Mutnovsky volcano. This stream flows beneath glacial ice on the flanks of Mutnovsky. Because glaciers on Kamchatka volcanoes have been melting in recent years, the roof of this cave is now so thin that sunlight penetrates through it, eerily illuminating the icy structures within.
Photo credit: Ivan Borovkov