Named for the obsidian sand that is common throughout this basin, Black Sand Geyser Basin is home to a plethora of steaming geysers and hot springs. This quick, 0.4-mile boardwalk tour starts at the parking area just west of Old Faithful and heads southwest. In 35 feet, turn right to access an observation deck overlooking Cliff Geyser, a sporadic, crater-like geyser. Next, cross a footbridge over Iron Spring and turn left on the boardwalk that leads to the deep greens of Emerald Pool, one of the park’s most well-known hot springs. Finish off the tour at the aptly-named Rainbow Pool whose multi-colored waters are caused by algae and cyanobacteria.
MORE PARK INFO Yellowstone National Park, (307) 344-7381; nps.gov/yell/
-Mapped by Jeff Chow