DIY Pinspiration: No instructions but this looks like so much FUN! Someone made a cat hammock/play center with PVC and a little fabric! Could start with these instructions & modify: http://www.instructables.com/id/Cat-TowerHammock/
Something a bit more elaborate than this leading up to our moon living room window? I could tie it into the tree-house theme I'm thinking of doing. It could just look like a platform tree house at the top of the "tree".