Keeping cats happy inside is simply a matter of creating a healthy and stimulating indoor environment. Some good ideas are giving your cat toys that feel furry or feathery or have catnip inside, providing him with a scratching post at least two feet high, planting pots of indoor greens for him to chew on, adopting another animal to keep him company, and, most importantly, playing games and spending time with your companion. Source: The Humane Society of the United States