Grand Prismatic Spring is the largest hot spring in the United States and one of the most famous features of Yellowstone National Park. Measuring about 370 feet (113 m) across and more than 120 feet (37 m) deep, it’s renowned for its striking rainbow-like rings of color — deep blue in the center, fading into greens, yellows, oranges, and reds at the edges. These colors come from heat-loving microbes called thermophiles, which thrive at different temperatures around the spring. The vivid bands, combined with the rising steam, create a surreal and otherworldly sight that embodies Yellowstone’s geothermal wonders.