Of the various mazes that the party can find in the PC role-playing game Planescape Torment, only the maze of evil Ravel has to be explored to complete the game. To reach the maze you will need to go through a long process of quests to find the correct portal key and the tools necessary to activate it.
Head to the Clerk's Ward in the city of Sigil and go inside the Civic Festhall in the northeastern corner of the area. Speak with the guard named Splinter at the front of the Festhall and ask him to join the Sensate faction.
Walk to the back of the Festhall and ask for a room. The woman at the desk will tell you that you already have a room. Go inside the room reserved for your party and get the "Dodecahedron" item from the closet.
Leave the Festhall and go the home of Finam the linguist and ask him to translate the writing inside the Dodecahedron. After he states that he cannot, use "Stories-Bones-Tell" special skill that The Nameless One has on the ashes of Finam's father. Ask the spirit of Finam's father to teach you to translate the language inside the Dodecahedron. Read the writing inside to get the code to a legacy you left behind on your last trip through Sigil.
Travel to the home of the advocate named Iannis. Give him the code for your legacy, and he will give the party several items and documents, one of which is a receipt for an item you commissioned the Godsmen to build.
Go to the Godsmen's foundry in the Lower Ward of Sigil. Give the receipt to the clerk inside and he will give the party a portal key. Leave the foundry and go to the Brothel of Slating Intellectual Lusts at the center of the Clerk's Ward.
Speak with the prostitute named Kessai-Serris and ask her if she is the daughter of the infamous night hag named Ravel. When she denies it, go talk to the prostitute named Kimaxsi and ask her about Ravel. Return to Kessai-Seris again and tell her that you know she is related to Ravel. Ask her to put a drop of her blood on a handkerchief.
Open up your inventory and use the portal key you got from the foundry. Use the blood of Kessai-Seris to activate the portal key and the party will then be transported to Ravel's Maze.
Once you go to Ravel's Maze you will be unable to return to the city of Sigil until the very end of the game, so make sure you have completed any quests in the city you want to before leaving for the maze.