Nestled in the Rincon Mountains south of Saguaro National Park, Colossal Cave Mountain Park is full of stalactites, stalagmites and flowstone, among other formations. It's a cool 70-degrees all year long.

It was built by the Civilian Conservation Corps during the Great Depression of the 1930s. Two companies of CCC workers housed at La Posta Quemada Ranch (now part of the park) improved the site, built the road and the stone buildings that are now listed on the National Register of Historic Places.