Iris USA 24" 4-Panel Exercise Pet Playpen With Door The Iris USA 24" 4-Panel Exercise Pet Playpen With Door ($35) is the perfect playpen for smaller dogs, and a great fit for apartment pet owners. It provides eight square feet of play space and a locking door, too. Image Source: amazon.com Iris USA 24" 4-Panel Exercise Pet Playpen With Door $35 from amazon.com Buy Now