It's first entrance is through the tutorial level, The Woods of Light, and is encounted at the very end after setting free the 4 Teensies. In this level, it's seen as a huge abyss which can only be opened if 5 Yellow Lums have been collected within the level. In each of the following levels however (excluding the Menhir hills, Prison Ship, Crow's Nest, and the 3 Sanctuaries) a small pad/shrine is used to hold the portal; which is summoned only by a dancing teensie, who can usually be freeed from a nearby cage.
The Teensies are the only ones who know how to get to the Hall of Doors. For the first time Rayman hears of this place, he will need 5 to enter the Hall of Doors. . When Rayman rescues one of the Teensies from a Pirate Cage, he will dance and then be out of the level. The Hall of Doors leads to many other levels once the levels before them are complete, which will allow Rayman to delve further to the Hall of Doors, until finally, Rayman reaches the main villain, Admiral Razorbeard.