Grotto Geyser is a fountain-type geyser located in the Upper Geyser Basin in Yellowstone National Park in the United States. Grotto Geyser is the namesake for the group of geysers that includes Grotto Fountain Geyser, South Grotto Fountain Geyser, Indicator Spring, Spa Geyser, Startling Geyser, and Rocket Geyser.