There isn’t really any hiking at Mammoth Hot Springs, just a boardwalk stroll, but it’s definitely worth a stop. Like most of the high profile spots in Yellowstone the parking lot gets pretty packed so stopping in the evening on the way back from Lamar Valley gives you great parking and great light. The boardwalk and railings are very important protections given the cavalier attitude of visitors to the park in the 19th and early 20th centuries. Carving into geysers, dropping coins and other personal objects into them, strolling around near the hot springs; the most notable picture of this kind of behavior was the posed photo of the Twenty-fifth Infantry Bicycle Corps on Minerva Terrace.