Old Faithful is Yellowstone National Park's most famous attraction. Here, just before dawn, it quietly steams as the pressure builds up below the ground in a series of caverns, later to be sprayed sometimes up to almost 200 feet into the air.
The heat of the Grand Prismatic Spring makes it home to a rainbow of bacteria. Here, the sunlight reflecting off of the blue and orange water illuminates the steam.
Two visitors to the Grand Prismatic Spring walk along the boardwalk suspended over the steaming hot spring waters.
