Rabbits are often inexorably drawn to bookcases, whether for the books, or for the interesting perching possibilities.
One of these days I would like to build Orion and Calypso Spots a fine play structure with several levels and areas to sit on and sit under. I'm afraid this project has been in the works for several years and not gotten anywhere yet, though. Whenever I go to a pet store and see the cat structures, I am quite jealous. But it does seems as though it would be relatively cheap and easy to build something appropriate to rabbits out of a selection of boards and with some fabric or carpet scraps stapled on.