|Inhabitants||Mutants, Frog-Dog, Reptilian Cook Reptilian Guards|
|List of all locations|
Castle Plun-Darr is the home and base of operations of the Mutants. The design for the castle is in the shape of a bat-like creature whose wings are designed to fold inwards to provide a double-shield to the main entrance. It is also surrounded by a moat. Unlike most traditional moats which contain sewage from the castle, this one serves as the castle's primary water source. However, the water is also infused with a substance called "Phosphor-R", which glows when disturbed to alert the Mutants of any intruders.
The head of the castle houses the main control room. The eyes serve as large windows.The mouth is designed to open and housed a cannon that could shoot fireballs. There was no automated targeting system, so it was necessary for a remote spotter near the target to call in trajectory corrections. The weapon, later destroyed by the ThunderCats, was made from salvaged parts from the Mutants' crashed space ship. In the chamber just above the head houses an execution device of the most brutal nature known as the Four Winds. It is an arrangement of four spring-loaded catapults designed to rip a person limb from limb.
There are escalators that go up to and down from the upper levels. There are also dungeons in the lowermost levels of the structure. The castle serves mainly as a garrison for the Mutants. The four chief ranking officers (Slithe, Monkian, Jackalman and Vultureman) each have their own quarters. All other mutants presumably sleep in barracks. The structure also houses a galley and Vultureman's laboratory.