The Grand Prismatic Spring is one of the most iconic and stunning geothermal features in the world. It is the largest hot spring in the United States and the third largest in the world, with a diameter of 370 feet and a depth of 121 feet. The spring is known for its striking rainbow colors, which are created by the unique bacteria that live in the mineral-rich waters. The colors are particularly vibrant during the summer months when the water temperature is at its highest. Take a boardwalk trail that leads around the edge of the spring for a closer view. One unique feature of the spring is its constantly changing colors, which shift based on the water temperature, time of day, and weather conditions. Despite its beauty, be careful to stay on designated paths and boardwalks, as the water can be dangerously hot and acidic.