Yellowstone National Park

Yellowstone National Park is located in Wyoming (and a little bit in Montana and Idaho). Directly to the south of it is Grand Teton National Park. Yellowstone is best known for the geysers (Old Faithful is just the best known of dozens) and other thermal features as well as it's bison herds.

My favorite part of the park is the Upper Geyser Basin, home to Old Faithful, Grotto Geyser, and Riverside Geyser. It is incredible the amount of thermal activity there is there and you can't find anything like it anywhere else in the United States. My next favorite is Grand Prismatic Spring. It is a large hot spring with blues, greens, yellows, and oranges. I hiked up to the hills above it and got a great view.

Geysers Old Faithful Geyser, Riverside Geyser, Oblong Geyser and others.
Midway Geyser Basin Cromatic Spring is big with bold colors.
West Thumb Geyser Basin Lots of thermal pools overlooking Lake Yellowstone.
Other Thermal Features Some pools, springs, and vents from Black Sand Basin, Upper Geyser Basin and Mud Volcano
Mammoth Hot Springs Towards the northern end of the park, a very large (you might even say mammoth) hot spring.
Animals Bison are everywhere but there are elk too.
Grand Canyon of the Yellowstone
Other sights in Yellowstone