By Alex Leviton

From upscale spa complexes to middle-of-nowhere swimming holes, any geothermally heated water can be called a "hot spring." However, not all of them are accessible, and fewer have the right combination of temperature (between 98 F and 104 F), minerals, safe conditions and free-flowing water to make them popular destinations. Here are a few hot springs to visit without bumping elbows with fellow soakers.

Dawn over St Marys Lake in the eastern Sierra Nevada region of California.
© Richard Cummins Lonely Planet Images.

Ojo Caliente, N.M.

Those in the know have called this New Mexico's best-kept secret for a few years, but those seeking its healing properties have been coming here for thousands. Modern health-seekers have resettled the outline of an ancient village by way of a resort, RV campground, restaurant featuring Southwestern cuisine and full-service spa. The only hot springs in the world to combine four distinct types of mineral waters – soda, lithium, iron and arsenic – Ojo Caliente is known for its curative properties as well as its historical significance. It's one of the first natural health hot springs resort in the United States, dating back to 1860. These days, visitors soak up the miracle cure as they lounge in mud pools, bask in private outdoor tubs or receive spa treatments.

Hot Springs, N.C.

There are only a handful of hot springs destinations east of the Mississippi, but Hot Springs, N.C., is one of the nation's best and most unsung. Plus, it's quite possibly the only place in the country where one can walk two city blocks of the Appalachian Trail, roast marshmallows over a campfire, get a massage, soak in a hot spring-fed Jacuzzi and hop into town for an art gallery walk or heirloom tomato salad in one afternoon. Fronting the French Broad River on the North Carolina–Tennessee border, Hot Springs is 45 minutes from the inimitable laid-back mountain town of Asheville, N.C., and about four hours from Atlanta, Raleigh, N.C., or Lexington, Ky.

Long Valley Caldera, Calif.

Leave the bumper-to-bumper traffic of Yosemite Valley behind for the high desert plains and soaring silver peaks of California's Eastern Sierra. The Long Valley Caldera, home to the resort town of Mammoth Lakes, was formed in a cataclysmic eruption 760,000 years ago and the effects are seen and felt to this day. Numerous natural hot springs, many on public land, dot the geologically active landscape. "Wild Willies" (a.k.a. Crowley Hot Springs) offers a man-made soaking pool fed by a clear-running, volcanically heated creek. There are no services nearby and your fellow hot springs enthusiasts might or might not be clothed (and that includes the nearby herd of cattle grazing on public land). To find this and other well-hidden swimming holes, grab a map at the Tioga Gas Mart (U.S. 395 at California state Route 120), where pleasantly surprised visitors can grab some buffalo meatloaf or lobster tacos (courtesy of a trained chef who fell in love with the Eastern Sierras and decided to stay) before their adventure.

Desert Hot Springs, Calif.

Not as glitzy as its glammed-up neighbor Palm Springs, Desert Hot Springs is the quieter (and quirkier) Coachella Valley cousin. Less than two hours' drive from Los Angeles, the area is well known for its boutique resorts and more casual atmosphere. There are still dozens of resorts to choose from, including RV parks, campsites, a juice-fasting retreat, an inn the style of a Marrakech riad and a few mid-century modern "spa-tels" from their heyday in the 1960s. Many hotels are fed with a constant stream of the area's mineral water that bubbles up under the entire town, judged in water-drinking contests – yes, there are such things – to be among the country's tastiest.

Bio: Alex Leviton is a Lonely Planet author and freelance writer living in San Francisco. She's a fan of most any natural body of water and, yes, she did once walk two city blocks of the Appalachian Trail.