Ultima Underworld: The Stygian Abyss is a first-person computer role-playing game (CRPG) developed by Blue Sky Productions (later Looking Glass Studios) and published by Origin Systems. It was released on March 27, 1992. It takes place in the fantasy setting of the Ultima series, inside the Great Stygian Abyss; a large, underground area that contains the remnants of a failed utopian civilization. The player assumes the role of series' protagonist "the Avatar" and attempts to find and rescue a baron's kidnapped daughter.
It was the first role-playing game to use true 3D graphics, and features many technological innovations, such as allowing the player to look up and down. It combines inspiration from earlier CRPGs like Wizardry and Dungeon Master with simulation elements, which led the game's designers to label it a "dungeon simulation". As such, the game is non-linear and contains emergent gameplay.
Ultima Underworld received widespread critical acclaim and sold nearly half a million copies. It was later placed on numerous "hall of fame" lists. A wide range of developers have claimed it as an influence, including Bethesda Softworks and Valve Corporation. In 1993, the game received a sequel, Ultima Underworld II: Labyrinth of Worlds.