Indoor kitties often enjoy surveying the scene from up high, so Walker has installed plenty of climbing posts wrapped in colorful sisal and cat ledges.

Wooden planks can be mounted to walls, providing cats with places to hang out.

A winding, colorful staircase enables Walker's cats to explore from all angles — and get in some exercise.

Walker recommends using Douglas fir or other dense wood when crafting ramps and perches for indoor cats.

The clever "mouse" hole in this wall leads to another room.

Providing indoor cats with ramps and toys can help stave off behavior issues.