Really ingenious and very good looking. Today I was looking at some really flimsy cat trees at Petsmart, really junk, and these are so sturdy. The cat looks exactly like one of my heart cats, Zoe.
I just use the big study free cardboard boxes from BJs. Right now I have a stack of 4 of them as a "cat tower". I don't have them glued to each other so the boxes occasionally do topple over when an energetic cat jumps in. I have a few other BJs boxes stacked to make "stairs" for the cats to get on the bed. They can jump just fine but I like to give them a lazy option.