Crystal Cave, Iceland

An ice cave is any type of natural cave (most commonly lava tubes or limestone caves) that contains significant amounts of perennial (year-round) ice. At least a portion of the cave must have a temperature below 0 °C (32 °F) all year round, and water must have traveled into the cave’s cold zone. This type of cave was first formally described by Englishman Edwin Swift Balch in 1900 who suggested the French term "glacieres" should be used for them, even though the terminology of "ice caves" was then, as now, commonly used to refer to caves simply containing year-round ice. More recently among speleologists "ice cave" has been proposed as the proper English language terminology and is in common usage today. A cavity formed within ice, is now properly called a glacier cave..
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