Planescape: Torment

Planescape: Torment is a role-playing video game developed for Microsoft Windows by Black Isle Studios and released on December 12, 1999 by Interplay Entertainment. It takes place in locations from the multiverse of Planescape, an Advanced Dungeons & Dragons (AD&D) fantasy campaign setting. The game's engine is a modified version of the Infinity Engine, which was also used for BioWare's Baldur's Gate, a previous AD&D game set in the Forgotten Realms.

Overview of Planescape: Torment:

Sigil... A place with gates that lead anywhere in existence, provided you have the proper key. It is a neutral ground and a watering hole for races across the multiverse, all under the watchful shadow of the Lady of Pain, the enigmatic ruler of the city. It is a place where the word is mightier than the sword, where thought defines reality, where belief has the power to reshape worlds and change the laws of physics...

But there's a lot more out there than just Sigil. Get outside the city and there's the planes themselves: the throne of the gods, the battleground of the eternal Blood War, and home to more horrors and wonders than ever existed on any Prime Material World. There's enough crusades, exploits, treasures and mysteries to keep a band of adventurers busy for centuries to come.

Anyways, all it takes is the right door, so step right through!

What's cool about Planescape: Torment:

An enthralling story, considered by many to be the best one ever told in a cRPG!
Professional voice acting, superb music, complex and gripping dialogue that covers over 5 000 pages.
Travel through the planes of the enormous and bizarre Planescape universe.