An Inside-Out Cave Hot Springs

 

Forty-five miles from the W. Entrance of Yellowstone National Park is Mammoth Hot Springs; also accessible and closer through the N. Entrance. It differs from all the other thermal areas because it is made out of soft-type rock called limestone. Due to its formations, the hot springs resemble a cave turned inside out. There's about 50 hot springs in the area. 

 

Upper Terraces

Lower Terraces

Mammoth Hot Springs
(map)