Carmel, California

Though not often thought of as a mineral springs destination, Monterey County has a few, and it recently debuted a new and sexy hydrotherapy experience. Refuge, billed as "America's First Co-Ed Relaxation Spa," features a hot-to-cold hydro thermal cycle. Start in a sauna or steam room, then plunge into a cool pool (or a cold one, if you have the nerve), relax on a lounge chair overlooking Carmel's scenic mountains...then repeat. Massages are also available for an extra charge.

Lena Katz is the senior travel correspondent for JustLuxe, covering trends, tastemakers, news and more.