An animal enclosure mountable in an access opening such as a window. The enclosure has a section extending to the building interior and an exterior section for containment of a litter box. Sealing member extends on the exterior of the enclosure and is engaged by a sliding window panel. The animal gains entry through a door in the interior section. A platform extends from the door along the window ledge. A low voltage fan unit draws air from the building interior into the enclosure.