The Trap Door is a puzzle/adventure game based on a TV show. The protagonist, a large blue creature named Berk, has to satisfy the needs of a mysterious entity known as "The Thing Upstairs" (only his voice is "heard" during the game).
The game was followed by Through The Trap Door, a sequel that was released in 1987.
In order to complete The Thing Upstairs' tasks, Berk needs to perform certain actions. For example: if the player is asked for a can of worms; they have to find the right container, catch the worms, put them into the can, then deliver the package upstairs. The objects are scattered around the castle in which the entire game takes place. The Trap Door features a hint system where a talking skull, named Boni, assists Berk whenever it's picked up.
The game features two difficulty levels (Learner & Super Berk). Learner difficulty is designed to help the player get used to the gameplay, players cannot actually finish the game on this difficulty; Super Berk features ghosts that will attempt to hinder Berk's progress.