icecaveerosion
Ice caves are cool! Here two rocks are perfectly nestled together. They probably fit well to begin with but have abraded each other to fit like a glove. Via a small pillar of ice, they are supporting the whole roof of the cavern I was in. Each of these rocks is less than a meter across. The roof is low enough that we had to crouch to move around, but this particular room was quite broad - perhaps 10 m across?