The most famous geyser in the world erupts roughly every 90 minutes, shooting a column of water 100 to 180 feet high for one to five minutes. The Visitor Education Center displays a countdown to the next predicted eruption, accurate to within about 10 minutes. The boardwalk around the geyser fills up quickly before each eruption; arrive 20 minutes early for a good spot. The wider Upper Geyser Basin — walkable from Old Faithful — contains more than 150 other geysers, including the predictable Castle, Riverside, and Grand geysers.
Old Faithful
A story
Old Faithful was named in 1870 by the Washburn Expedition — the first government-sponsored survey of Yellowstone — making it the first geyser in the park to receive a name. The explorers chose "faithful" because it erupted with unusual regularity, and that reputation has held ever since. The average interval between eruptions has actually lengthened over time: it was around 66 minutes in the early 20th century and is now closer to 90, a shift geologists attribute to changes in underground water levels after a 1998 earthquake.