Fodor's Expert Review Grand Prismatic Spring

You can reach Yellowstone's largest hot spring, 370 feet in diameter and arguably an even more dazzling sight than Old Faithful, by following a ⅓-mile boardwalk loop. The spring, in the Midway Geyser Basin, is deep blue in color, with yellow and orange rings formed by bacteria that give it the effect of a prism. For a stunning perspective, view it from the overlook along the Fairy Falls Trail.