It has been very interesting reading everyone's comments/viewpoints... As Pieper's Mom mentioned, "habi-cat" structures look like a good way to give a cat an "outdoor" experience. I have seen a large habi-cat attached to someone's house and there were at least two cats lounging in it, looking like they were having a grand old time, getting some sun through the screens, and being able to see the sights and smell the smells. I think window sills are perfectly good, too. I agreed with those who wrote about making the indoors more attractive to cats than the outdoors. I can give my cat plenty of exercise inside, making her run and jump when I play with her and entertain her with toys (I think I would like to try the laser pointer!). If a cat is in the habit of going outside and you want to help it "quit", maybe just distracting it by engaging it in playtime would really help.