According to the National Park Service, "Grand Prismatic Spring, located in Midway Geyser Basin, has the distinction of being the park’s largest hot spring. It measures approximately 370 feet (112.8 m) in diameter and is over 121 feet (37 m) deep. A description of this spring by fur trapper Osborne Russell in 1839 also makes it the earliest described thermal feature in Yellowstone that is definitely identifiable."

If you can't find parking at Midway Basin to see Grand Prismatic at eye level, then take a hike along the Fairy Falls Trail, detouring up to the Grand Prismatic Overlook for a view not only of the park's largest hot spring, but of the land around and beyond. FYI, early mornings and late afternoons offer the best lighting for photos.