While soaking in Old Faithful’s 244°F waters would spell a certain death, Yellowstone—which sits above a 300-mile-wide ocean of magma—is home to a few natural spas the mix with creeks, making them worthy of a post-hike dip. Your best option? Ferris Fork and Dunanda Falls.
Located in the southeast corner of the park, Ferris Fork and Dunanda Falls requires a 15-mile approach from the Bechler trailhead. You’ll follow the Bechler through dense stands of lodgepole pine that give way to the sheer walls of Bechler Canyon. Look out for Ragged Falls, named for its spaghetti-like 5-foot cascade, and Twister Falls, which coils 55 feet downward from its flume. Detour through Bechler Meadows to 150-foot Dunanda Falls, which spills into a basin, creating several soakable pools (averaging 110°F). Find a designated campsite back of the banks.
Thirsty for more? Back on the main trail, continue 6 miles northeast to Three Rivers Junction (where the Phillips, Gregg, and Ferris Forks converge). Follow the worn user trail to a steaming pool hidden along the bank of the river. After simmering, continue upstream to cool off below Gwinna and Sluiceway Falls. (Option: Camp below 260-foot Albright Falls).
Do it Find the trailhead at the end of unpaved Cave Falls Rd., 26 miles outside Ashton, ID.
Permits Reserve campsites at the Yellowstone Backcountry Office (307-344-2160) or go on a guided trip.