I am an owner of 2 beautiful cats, Gaia and Isis, they aren't related at all, but they grew up together so they really like each others, they play and enjoy being together. I allow them to jump, run and play inside the house. They have already destroy a vault/bench by scratching their nails.. I've always thought of adding some mods to my apartment so they can climb and be more playful while being inside a house.

Here's a video with some ideas, I mean you don't have to purchase them, just let your creativeness to flow...