Old Faithful is a deceptively useful natural wonder - it only offers a +2 Science bonus if worked, but provides +3 Happiness just for being in your territory. However, considering how rare Science bonuses are in the early game, a civilization that acts quickly could make good use of this wonder.
Old Faithful also counts as a mountain for movement purposes and purposes of building an Observatory. Only Helicopter Gunships can enter its tile, and they sustain damage if left there as if it were a mountain.
Old Faithful is a geyser found in Yellowstone National Park, in Wyoming, US. First seen by Europeans in 1870 (and by natives some 10,000 years before that), Old Faithful was thus named because of the regularity of its eruption. The geyser shoots a column of boiling water to a height of some 30-50 meters (100-175 feet) every 60-90 minutes (the interval determined by the ferocity of the previous eruption). Geysers occur when subterranean water hits magma (molten rock). The water is instantly turned to steam, which rushes out the nearest available opening at tremendously high pressure. Old Faithful and the other 250 geysers in Yellowstone are enjoyed by some three million visitors each year.