Abstract: Shelves for assembling climbing apparatus on the walls of a building, for affording exercise and amusement to climbing pets such as cats. Each shelf has a horizontal platform and a vertical depending flange. The platform and flange have common flat rear surfaces. The flange has holes for accepting fasteners for mounting the shelf to the wall. Both the platform and the flange have rounded corners. The platform has a downwardly open, blind threaded hole for receiving a hook or the like, for suspending objects from the shelf. Preferably, the shelves are provided in sets or kits of at least three shelves differently configured from one another. One difference is that of relative widths. Another difference is that one shelf is configured to cooperate with a corner formed by intersecting walls of the building.