What could I add to the cog ( dog & cat ) condo I built?

Well it's not much but, I used two card board boxes. I cut off one side of each and put one into the other, I taped it up so it's nice and stable. I then, carved a door into the front and made two windows. I made a good sized hole in the side of the front box and I put the part of a plastic hanger where it curves into the hole. On that, I tied a string with a feather tied to it. Im going to put a blanket inside, maybe add another level.... I don't know what else to do. Sorry there is no pic. My cat loves it but my mini dachshund is scared to go inside. I want it to be comfortable for both. What to do? Thanks.