Excelsior Geyser, Thermal pool in Midway Geyser Basin, Wyoming, US.

Excelsior Geyser is a hot spring in Midway Geyser Basin with a deep crater-like pool filled with brilliant blue water. Hot water flows continuously from the basin, creating steaming channels that wind through the surrounding ground.

Excelsior was named by Yellowstone superintendent P. W. Norris in 1881, not by the 1871 Hayden survey. It was first reported in 1869 as a crater showing signs of past eruptions, but eruptions were not seen until 1881, when water rose 100 to 300 feet. After 1888 eruptions, its plumbing was damaged and it became a hot spring; it erupted again for 46 hours in September 1985.

P. W. Norris, Yellowstone's superintendent, named it in 1881; the name comes from the Latin for "higher" or "loftier." Visitors today see the crater as a steaming blue pool discharging hot water into the Firehole River, with bands of yellow, orange and rusty brown staining the ground along its right edge.

The pool sits in the Midway Geyser Basin, reached by a curved walkway that passes above it; the boardwalk keeps visitors off the white and grey mineral crust. Its water is 93 °C (199 °F) and discharges 4,000 to 4,500 gallons per minute into the Firehole River, so stay on the path and keep back from the steam.

Two photographers, F. Jay Haynes and T. W. Ingersoll, recorded the violent eruptions of spring 1888, not a single image by one person. Their photographs document the outbursts that by the end of that year had the geyser reported as extinct.