if cats can be treated like dogs, bring them for a walk outside, that would be fun for them i think. but cats are more of lazy walkers, they wont walk when we force. i sometimes tie a long string to my cat's collar and let him play outside my door. so he has the chance to be curious and explore the place outside. but everytime people come, he will run into the house because he is scared of unknown faces and places. i think its okay to let them free a bit because they know where to come back later. but u have to frequently check on them.