What an awesome idea! This would be great built in a kids walk-in closet! Just take the doors off the closet and utilize the extra space! Keep the kids clothes etc in a wardrobe in front of the closet to make it a secret hideout!
I love this under stair indoor "dog house." Its out of the way and it even has a window. What more could a dog want? I do want this somewhere,so that while we are gone,they can look out of "their window" and watch for our return.