An open area where he can run around is probably best. Depends on where you live and your cat’s preferences. I’ve heard of cats that have no desire to leave the house and others that will dart out the door at any opportunity. If you have an apartment or no fence in the back yard then it’s not a great option. Some cats do like to walk, our neighbors’ cat usually joins us on our nightly walks through the neighborhood. Off a leash of course.