One of the most popular hikes in Yellowstone is the Fairy Falls trail. It is a little over 5 miles if you just got to the falls. If you add Imperial Geyser it is about 7 miles round trip. I have been out there twice. The first time by myself and the second with Donna once I let her know that it is a almost completely flat trail.
I want out there alone to get more miles for the 100 miles club. This trail has so many folks on it you can hike alone. You really won’t be alone. There was a person within 10 feet of me the entire hike. I think this is so popular because the beginning of this trail has the overlook to Grand Prismatic which is the Mid Geyser Basin region. You can also bike part of this trail. It is also very family friendly since it is flat. I highly recommend going the extra 3/4 miles to Imperial Geyser. There is a pool, geyser and mud pots back there. It is extra cool to be in that area.
My first time to the falls:
My second time to the falls: