The Trap Door

A series focusing on the monsters living in an isolated castle and the caverns beneath it, within unspecified "dark and nasty regions" of the world. The main character is Berk, the overworked servant of "the thing upstairs" who is the castle's owner. The owner is an unseen character who isolates himself in the attic of the castle. He merely shouts orders to Berk, and regularly demands food. Berk habitually leaves the castle's trap door open, inevitably allowing bothersome creatures from the caverns to enter the castle. Some are genuinely hostile to the residents of the castle, others are friendly but irritating.