Mildew's House does not appear to be partitioned into rooms in the interior. It has a flat-topped stone serving as a bed, with a hollow underneath as a space for Fungus to sleep. There are various things hanging from the rafters and walls including various unused weaponry and dragon body parts. He also has a mural of a dragon killing on the wall, as well as portraits of his three deceased wives, and one of Fungus.
Mildew's House is situated up against the rock on the back side of the Great Hall's spire. It is a simple design with a severely sloped roof like most of Berk's homes, and adorned with a dragon head reminiscent of a Deadly Nadder at its entrance. There is also a ramp leading up to the door. In front of it is a field used solely for Cabbage. The roof is fairly unkempt and has Ivy growing on it.
Mildew's House serves as shelter and residence for Mildew and Fungus, protecting them from the outside elements.