An hour went by in a flash, and Jareth and Aria walked continuously and reached the end of the long path.
Unlike the other floors of the dungeon, the fifth floor had no mazes or monsters residing in it.
The only monster on this floor is the dungeon master.
The final floor is basically the 'home' of the strongest beast in this whole dungeon; thus, no other monster is allowed to wander around in its home.
As a result, after walking for a while, Jareth and Aria arrived directly at the giant door of the final boss room.
Most dungeons in this world follow the same pattern; the final floor in most dungeons is relatively empty, and only the final boss resides there.
Strong monsters are extremely protective of their territories; after all, they won't let random monsters wander around in the place that they live and consider their home.