Ultima Underworld: The Stygian Abyss is a first-person role-playing video game developed by Blue Sky Productions (later Looking Glass Studios) and published by Origin Systems.

It takes place inside the Great Stygian Abyss: a large cave system that contains the remnants of a failed utopian civilization.

Ultima Underworld has been cited as the first role-playing game to feature first-person action in a 3D environment, and it introduced technological innovations such as allowing the player to look up and down.

The player attacks by holding the cursor over the game screen and clicking, depressing the button longer to inflict greater damage.

[1] The game was designed to give players "a palette of strategies" with which to approach situations, and its simulation systems allow for emergent gameplay.

To achieve this, he united diverse cultures and races in peaceful co-existence and planned to promote harmony by giving each group one of eight virtue-imbued magical artifacts.

[11] At the time of Ultima Underworld, the Abyss contains the remnants of Cabirus's colony, inhabited by fractious groups of humans, goblins, trolls and others.

[11][12] Before the beginning of the game, the Abyss-dwelling wizard brothers Garamon and Tyball accidentally summon a demon, the Slasher of Veils, while experimenting with inter-dimensional travel.

[2] A few possible scenarios include deciding the fate of two warring goblin tribes, learning a language, and playing an instrument to complete a quest.

[13][18] However, as he dies, Tyball reveals that he had decided to contain the Slasher of Veils, whose prison he had been weakening, within Arial as a way to prevent it from destroying the world.

Neurath had enjoyed role-playing video games like Wizardry, but found that their simple, abstract visuals were an obstacle to the suspension of disbelief.

[20] He believed that Dungeon Master's detailed first-person presentation was a "glimpse into the future", and he sought to create a fantasy role-playing game that built on its example.

[20] In early 1990, Neurath wrote a design document for a game titled Underworld,[19] which described such elements as "goblins on the prows of rowboats tossed in the waves, shooting arrows at the player above on a rope bridge swinging in the wind.

Neurath had experimented unsuccessfully with the concept on an Apple II computer in the late 1980s, but he believed that the more powerful IBM PCs of the time might be able to process it.

[19][20][23] Using the Space Rogue engine, Green's algorithm, assembly code from Lerner Research's Car and Driver and original programming, the Blue Sky team completed a prototype of Underworld after roughly a month of work.

[7][10][20][23] Neurath described the prototype as "fast, smooth, and [featuring] true texture mapped walls, though the ceiling and floor were flat shaded and the corridors and rooms were all 10' [3.0 m] high—it looked a lot like Wolfenstein-3D in fact.

[20] According to Schmidt, Neurath contracted a writer to create the game's story and dialogue, but the relationship was a "mismatch"; and so the team decided to write the plot themselves.

He noted that the team had "no set of rules ... or pre-written plan", but rather worked organically toward the general idea of creating a "dungeon simulation".

[21] Certain failed experiments meant that the team created "[AI] code for many ideas which turned out to be largely irrelevant to the actual gameplay".

"[7] We had about eight of us in this 15x15 room, sitting in uncomfortable red deck chairs, faxing bug lists to Origin and back, blasting music and playing Monkey Island II about 30 minutes a day to avoid insanity.

[10][22] The team hired college friends such as Marc LeBlanc to bug test the game,[25] and Spector stayed at the studio for roughly a month and a half, according to Church.

[10] Neurath summarized, "Despite the austere working environment, the game came together amazingly well in the final stretch, and we delivered the Gold Master just about two years after we had started.

The engine allowed for transparencies, walls at 45 degree angles, multiple tile heights and inclined surfaces, doors that swung open and closed, and other aspects.

[36] ACE called Ultima Underworld "the next true evolutionary step in the RPG genre", and noted that its simulation-style dungeon was "frighteningly realistic".

The magazine thought that the game's sprite character models "detract from the dense atmosphere a bit", but ended the review by stating, "If you've got a PC, then you've got to have Ultima Underworld.

"[31] Ultima Underworld was inducted into many hall of fame lists, including those compiled by GameSpy, IGN and Computer Gaming World.

[59] Toby Gard stated that, when designing Tomb Raider, he "was a big fan of ... Ultima Underworld and I wanted to mix that type of game with the sort of polygon characters that were just being showcased in Virtua Fighter.

[61] In the book Masters of Doom, author David Kushner asserts that the concept was discussed only briefly during a 1991 telephone conversation between Paul Neurath and John Romero.

[64] On March 14, 1997, a 3D remake of the game (published by Electronic Arts Victor) was released exclusively in Japan for the PlayStation by Infinity Entertainment.

[66][67] In 2015, Otherside Entertainment, a new developer founded by Paul Neurath and other Looking Glass and Irrational veterans, announced a new entry in the series, entitled Underworld Ascendant.