Idaho’s Mammoth Cave is the largest volcanic cave in the world open to the public.
Grab a lantern from the proprietor for a self-guided tour on a boardwalk deep into the lava tube cave. It is not an ice cave, but probably was one for hundreds of years before the vegetation covered the black rock. It maintains a temperature of 41 degrees during both the winter and summer months. Adjacent to the cave is the Shoshone Bird Museum, a taxidermist’s heaven.