Dig the possibility of a built in ball or water toy. Thinking that a peg-board or similar on the wall (outside, inside, both) would give us some flexibility here. I just realized this is a cat play house, but the one
AWESOME homemade cat scratcher tree, made from scrap wood and recycled stuff! And my favorite part is, this whole thing securely attaches to the wall, so they can roughhouse as much as they want. Now I just need a new cat.