Old Faithful
Yellowstone National Park, Wyoming
Generations of tourists traveled to Yellowstone National Park for two reasons: to feed bears from the comfort of their cars, and to watch Old Faithful the geyser. The bears no longer mooch from cars -- in fact, tourists are officially forbidden from getting within 100 yards of a Yellowstone bear -- but Old Faithful keeps going, erupting in a plume about 150 feet high every 90 minutes or so, soaking visitors when the wind is right.
Nature is rarely this accommodating or predictable, which has earned Old Faithful many fans, even though Yellowstone has taller and bigger geysers.