Our family includes a couple house cats.  We also foster kittens for a local shelter to get them socialized prior to adoption.   So it's not uncommon for there to be 4 cats in the house at any given time.  While the kittens are getting acclimated to their surroundings, they're usually confined to our family room/kitchen.  I've been wanting to build some kind of climbing structure for them for a while, but haven't started until now for a couple reasons:

As I started thinking about this project again recently, I identified 2 places in the room where I could put something, but the structure would need to be fairly shallow so as not to overwhelm the space. 

I started thinking about those tension pole caddies that everyone's grandma used to have in the bathroom - something like this:

Now I could probably pick one of these up on trash day somewhere within a 5 mile radius and just call it a day.  However, it's butt-ugly (pun intended) even though it's probably considered mid-century modern.  But I liked the idea of the tension poles to stabilize a shallow structure.  I started googling for other inspiration images that were mid-century modern and made of wood.  Where I landed was on a modular bookcase/room divider by an Italian designer named Franco Albini back in the mid-50's.  Here's an example of the design from 1stdibs.com:

I've started this project without a clear picture of the actual climbing components, but I know I'll begin by building two uprights based on this design.  If it doesn't work out as a cat tree, I can always repurpose it.  As a bookcase, for example.