Check out The K&H Pet Products Door Hanging Cat Condo

The unit simply hangs on the top edge of a door, as a hanging shoe rack would, and provides five levels that cats access through seven holes located on the front and two sides of the condo.

Hangin' Cat Condo - like the idea of hanging something on a door for the kitties (space saving!)

The is a great way to give your cat plenty of hiding spaces if you live in a condo or apartment where space is limited. It’s no secret that cats love to climb, and they especially enjoy cat trees. The Hangin’ Cat Condo mimics a cat tree, but is hung on a door to save space.

Over the Door Hanging Cat Condo -Craziest Gadgets

NEW Hangin' Hanging Cat Condo K&H Pet Products Small Door Tree House Tan My #1 pick is not a cat tree. Instead, it is the hanging cat condo from K&H manufacturing. This is a beautifully designed space-saving cat condo that can be mounted on just about any door. The best part is that despite looking like it’s quite compact and limited in space, it boasts of five interconnected levels with seven openings that your cats can access and jump out of.

Shop for New Cat Condos Door Hanging Scratcher with Sisal Rope

Products & resources mentioned in the video: Back of the door cat climber: Hanging cat condo for door: Window-mounted cat bed: The ultimate cat climbing post: Waterproof mattress cover: Sisal rope

Door-Hanging Feline Abodes : cat condo - Trend Hunter