Big Ice Cave in Montana is a single chamber of the ice cellar type. It’s morphology results in a cold trap, a physical effect that is the reason why this cave contains ice and icicles year round, and (obviously) is the reason for its name. In the simplest terms, in winter cold air "flows" into the cave; in summer it stays there, since cold air is heavier than warm air.

The cave is not a show cave, though it is, in a way, developed. There are no guided tours or speleothems, but a short walk down a plank trail into the entrance portal and onto a wooden platform inside the cave allows visitors can see the ever-present ice floor of the cave. Bring a jacket.