Steamboat, the world's largest active geyser (and one of the most unpredictable), is in Norris Geyser Basin. Scientists believe this basin has been active for 100,000 years, making it the oldest geyser basin in the park. It's also hot: In 1929, a team of scientists measured the temperature 1,087 ft/335 m below the surface at 459 F/237 C. The interval between geyser eruptions ranges from four days to 50 years, so be patient. At Norris, on the Grand Loop, Yellowstone National Park. http://mms.nps.gov/yell/features/norristour/index.htm.
