Ultima Underworld: The Stygian Abyss

Ultima Underworld is a first-person role-playing video game. It takes place inside a large, underground cave.It has been cited as the first RPG to feature first-person action in a 3D environment, and it introduced technological innovations such as allowing the player to look up and down. Its design combines simulation elements with concepts from earlier CRPGs which led the game's designers to call it a "dungeon simulation". The game is non-linear and allows for emergent gameplay.