Although cats have long been housed indoors to protect them from the dangers of the outdoor environment, such as infectious agents and physical trauma, this is a fairly recent cultural development in North America. In fact, indoor “captivity” can be hazardous to cats if their environmental needs are not met.
The following list is not all-inclusive, but examines 5 general ways to enrich an indoor cat’s environment:
Enhance Basic Resources
Provide Ample Physical Space
Offer Outlets for Normal Behavior
Respect Social Interaction Limits
Facilitate Sensory Stimulation
Check out this PDF for detailed information