Natural Bridges is one of the most magical swimming spots in California's Gold Country — a pair of massive limestone caverns that Coyote Creek has tunneled straight through the hillside, forming natural rock bridges you can actually swim and float beneath. Hidden in the oak-covered foothills of Calaveras County near Vallecito (between Sonora and Angels Camp), it's a beloved local secret and, unlike most of the region's show caves, completely free and open to the public.

The reward takes a bit of work to reach. From the trailhead off Parrotts Ferry Road, a roughly 2-mile round-trip hike drops down through the hills to the creek and the mouth of the cavern. Along the way you get views of the surrounding country, and the trail continues up and over the top of the bridge for those who want to explore both the water below and the formation above.

At the creek, the real adventure begins. Coyote Creek flows right through the 250-foot travertine cavern, and depending on water levels you can float or swim through the tunnel from one end to the other, drifting through cool, dim chambers and deep green pools with the limestone arching overhead. On a hot Sierra-foothills summer day it's an unforgettable experience — part swimming hole, part cave exploration — and many people bring inflatables to float the passage.

Go carefully, and help protect it. The rocks are slick, the water depth and current change with the season (the creek can run high and cold in spring), and swimming through a dark cavern carries real risk — only go when the water is calm and low enough, never alone, and check depth before jumping anywhere. Just as important, this is a living limestone formation: the oils on human skin, along with graffiti and litter, genuinely damage it, so avoid touching the cave walls where you can, pack out every scrap of trash, and tread lightly. The site is cared for by the Bureau of Reclamation and conservation groups precisely because heavy use threatens it.

There are actually two bridges — an upper and a lower — and Coyote Creek eventually flows on to New Melones Lake. The whole of Calaveras County is honeycombed with caves and caverns, most of them commercial show caves you pay to tour, which makes this free, wild swim-through all the more special.

Timing and preparation matter. Summer into early fall is the prime, safest window, when the creek is low and warm; it also draws crowds, so arrive early. Wear sturdy shoes with grip for the rocky trail and slick cavern, bring water and sun protection for the exposed hike, and consider water shoes and a light for the swim-through. Come respectful and prepared, and Natural Bridges delivers a genuinely rare thrill — swimming through a cave carved by a creek, in the heart of California's historic Gold Country.