From the outside, it's hard to tell The Crater at Homestead Resort even exists. You can only see the 55-foot limestone mound that sits over it, offering shelter and protection. But peer down through a hole in the stone—the same one that lets in sunlight and fresh air—and you'll discover an entire world below. It's a pool of snowmelt that gathered 2 miles deep in the ground over the past 10,000 years before percolating upward and gathering minerals along the way. The earth itself heats the water and the air around it to about 90–96 degrees. Guests walk through a tunnel at ground level to get to the geothermal pool, where they can swim and explore, scuba dive, snorkel, or take a yoga class atop standup paddleboards.