Colossal Cave, Show cave and museum in southeastern Arizona, United States.

Colossal Cave is a dry karst cave near Vail, Arizona, with about 3.9 miles (6.3 km) of mapped passages. Its limestone formations are no longer growing because the water that created them now feeds nearby Arkenstone Cave. The photograph shows a tall, wet-looking tan and ochre rock column rising from a dark floor, surrounded by similar cave rock.

Colossal Cave was used from 900 to 1450 AD by the Hohokam, Sobaipuri and Apache. In January 1879 Solomon Lick and companions explored about 500 feet inside what they took for an old mine or cave, finding bat guano, old ashes and some 500 deer antlers. By 1890 William Shaw and soldiers from Fort Lowell explored it for five hours by candle and magnesium wire light.

The name Colossal Cave was reportedly coined in 1917, when amateur spelunker Lynn Hodgson surveyed the cave for Alfred A. Trippel and declared it "colossal." Others credit Byron Cummings of the University of Arizona. Earlier names were Mountain Springs Cave and Five-Mile Cave.

The cavern stays at a steady temperature throughout the year, so visitors should dress appropriately for cool underground conditions. Guided tours are offered regularly and can accommodate different fitness levels.

In 2025 a team led by Dalton Carper remapped Colossal Cave and found about 0.4 miles (0.64 km) of passages and rooms undocumented since 1987, including a chamber holding water in a system long treated as dry. The cave holds roughly 3.9 miles (6.3 km) of mapped passageway.