Abstract: The edge surfaces of a terrarium floor are adhered to side walls of an aquarium tank. A terrarium compartment has a triangular cross section formed by the space above the terrarium floor and part of the side walls of the aquarium tank. The forward edge of the terrarium floor is spaced from the front or the side wall of the aquarium tank to form an opening therebetween of sufficient size for access to the body of water below the terrarium floor and movement of an amphibian between the body of water and the terrarium compartment. In a further embodiment, the terrarium compartment further includes a terrarium side wall adhered along the bottom edge to the terrarium floor to form an upwardly-extending barrier wall and thereby defines the terrarium compartment with a cross-sectional shape of a keystone.