Niter Ice Cave in Grace, Idaho

An opening of an ice cave made from molten rock was mentioned in 1898 when a settler family used it to store milk and butter. The entire cave was formed by lava some 500,000 years ago. 

Today, Niter Ice Cave is mostly a roadside attraction. It's located about a hundred yards from the main road, and a painted sign announces its location. You can usually find a few icicles forming where water drips down from the top of the cave.