In the old British children's show of the same name, the Trap Door refers to an actual trap-door found in the cellar of Berk's castle. Beneath this door lies a series of underground catacombs that run all under the Dark and Nasty Regions which are home to all manner of strange creatures. On a regular basis, these monsters would emerge from the trap door into the castle, causing trouble for Berk and his friends. Sometimes Berk leaves the trap door open after throwing garbage down there and creatures find their way up through it, other times they just force the door open anyway. There have also been times when Berk and friends have gone down the trap door themselves, though usually not by choice. The layout of the caverns beneath the trap door has never remained consistent, the underground world beneath the castle always seems to change each time Berk has had the misfortune to find himself down there.