Old Faithful may be more famous, but the Grand Prismatic Hot Spring is the most photographed thermal feature in Yellowstone. That’s because of its crazy-bright colors and enormous size. The Grand Prismatic Spring is the largest hot spring in the United States. Its colors match most of those seen in the rainbow dispersion of white light by an optical prism: red, orange, yellow, green, and blue

While we were there, steam covered the Grand Prismatic and did not reveal its brilliant colors, but adjoining springs were equally colorful and will be posted next.