Notice the little square hole in the wall on the right side of the door near the floor. This is the cat door. Our cats are in-door / out-door cats. That means they come and go as they please during the day...at least as much as Scott and I are willing to let them in and out. But, at night, they are inside.
A quandary related to cats is where to put the litter box. Not in the bedroom certainly. We opted for one of the storage rooms in Scott's office. While our cats are absolutely smart enough to learn how to open the office door, which will usually be closed, we are not inclined to teach them. As an alternative, we provided this door. You'll notice, in the photo above, there is no trim on the cat door yet.