We also have a “Kitty Peeper” that we purchased from http://www.catswithanaltitude.com. It is on our second floor and is installed in a window. It basically looks like an air conditioner from the outside but is actually a nice little cubby for the cats to lay in and look outside plus get some fresh air. There are nice plastic flaps where the cat enters on the inside of the house and it is lined with green astroturf.
The pictures below are not of our peeper but from the website where you can purchase this item. http://www.catswithanaltitude.com