The Treasure of Mockingbird Heights (S02E14)

During a raging thunderstorm, the lights in the Munster house go out and Herman and Grandpa go to the dungeon in search of the fuse box. While groping along the walls in a seldom explored part of the cellar, Herman accidentally discovers a hidden door that opens and reveals a secret room equipped as a torture chamber. As Herman and Grandpa search through the room, they find a map that apparently reveals the hiding place of a pirate's secret treasure. (iTunes)