Firehole Canyon Drive is a 2-mile, one-way side trip along the Grand Loop Road just south of Madison Junction. The main features of this road are the striking canyon cut through 800-foot lava flows, a nice 40-foot waterfall, and one of only two swimming holes in Yellowstone National Park.
After leaving the main park loop, the one-lane road winds through the Firehole Canyon with occasional turnouts to get out and view the canyon. The falls are not very high, but they are nicely placed in the canyon with overlooks. A bit farther down the road is the Firehole Canyon swimming hole. The river widens here and forms a safe swimming spot, though there are no lifeguards on duty here. There are restroom facilities and a small beach as well.