Yellowstone National Park is a nearly 3,500-sq.-mile wilderness recreation area atop a volcanic hot spot. Mostly in Wyoming, the park spreads into parts of Montana and Idaho too. Yellowstone features dramatic canyons, alpine rivers, lush forests, hot springs and gushing geysers, including its most famous, Old Faithful. It's also home to hundreds of animal species, including bears, wolves, bison, elk and antelope. The Grand Prismatic Spring in Yellowstone National Park is the largest hot spring in the United States, and the third largest in the world, after Frying Pan Lake in New Zealand and Boiling Lake in Dominica. It is located in the Midway Geyser Basin.