Penn-Plax's Reptology Rockies Terrarium Backgrounds are designed to take reptiles to the mountain top by transforming a terrarium into a rocklike environment, the company states. Designed to fit Reptology terrariums and most other major terrarium brands, the realistic background also can be used to create a stunning waterfall display and a natural vivarium, the company adds. The backgrounds are available in three sizes—12 in. x 18 in., 18 in. x 18 in. and 24 in. x 24 in.—and can be trimmed to fit smaller sizes.