The floor space is quite small, so we built a series of platforms all the way to the ceiling to make room for more cats.
We used three colors of acrylic rods in a spiral pattern, illuminating them with LEDs concealed in the platforms.
Each platform has a semi-enclosed space for a cat defined by the acrylic rods and a round cushion.
The cat on the very top platform is a stuffed pillow. The other cat thinks this is plenty high enough.
Sunlight shining through the rods makes interesting shadows on the adjacent wall. Another wall in the house also gets washed with color when the light is right.