Colossal Cave Adventure (also known as Adventure or ADVENT) is a text-based adventure game, released in 1976 by developer Will Crowther for the PDP-10 mainframe computer. It was expanded upon in 1977 by Don Woods. In the game, the player explores a cave system rumored to be filled with treasure and gold. The game is composed of dozens of locations, and the player moves between these locations and interacts with objects in them by typing one- or two-word commands which are interpreted by the game's natural language input system. The program acts as a narrator, describing the player's location and the results of the player's attempted actions. It is the first well-known example of interactive fiction, as well as the first well-known adventure game, for which it was also the namesake.

The original game, written in 1975 and 1976, was based on Crowther's maps and experiences caving in Mammoth Cave in Kentucky, the longest cave system in the world; further, it was intended, in part, to be accessible to non-technical players, such as his two daughters. Woods' version expanded the game in size and increased the number of fantasy elements present in it, such as a dragon and magic spells. Both versions, typically played over teleprinters connected to mainframe computers, were spread around the nascent ARPANET, the precursor to the Internet, which Crowther was involved in developing.

Colossal Cave Adventure was one of the first teletype games and was massively popular in the computer community of the late 1970s, with numerous ports and modified versions being created based on Woods' source code. It directly inspired the creation of numerous games, including Zork (1977), Adventureland (1978), Mystery House (1980), Rogue (1980), and Adventure (1980), which went on to be the foundations of the interactive fiction, adventure, roguelike, and action-adventure genres. It also influenced the creation of the MUD and computer role-playing game genres. It has been noted as one of the most influential video games, and in 2019 was inducted into the World Video Game Hall of Fame by The Strong and the International Center for the History of Electronic Games.