In Aincrad, Labyrinths are tower-like structures with many floors that connect each Aincrad Floor to the next and are found on every floor. The entrance to each Labyrinth is guarded by a Field Boss, strategically placed in such a way that the Labyrinth could not be accessed until this boss is defeated. The Boss Room of a Labyrinth must be found on the topmost Labyrinth level and cleared before the stairs to the next Aincrad Floor are opened.