Kirkham Hot Springs, Boise National Forest

Kirkham Hot Springs is the kind of place that makes Idaho's Highway 21 famous. The U.S. Forest Service describes pools and small steaming waterfalls set right against the South Fork Payette River, just east of the tiny town of Lowman in the Boise National Forest at roughly 4,000 feet. A short trail with staircases drops from the parking area down to the riverbank, where the geothermal water mixes with the cold river.

What makes this a standout RV route is the byway itself. Highway 21, the Ponderosa Pine Scenic Byway, threads a whole corridor of roadside hot springs through the Boise National Forest about 74 miles northeast of the city. Kirkham is one of the easiest to reach, but a single drive can pass several, with the South Fork and Main Payette also drawing whitewater rafters and kayakers through the canyon.

The site is managed for day use, open 7 a.m. to 9 p.m. with a modest per-vehicle fee and no overnight camping at the springs. That keeps Kirkham as a stop rather than a basecamp, so RV travelers typically pair it with developed Forest Service campgrounds elsewhere on the byway. Pulling in for an afternoon soak with the river rushing past is about as classic an Idaho road-trip moment as there is.