I've got this friend who's looking for well-designed cat furniture  

I know what you mean, Olive--
I'm sorely tempted to install the kitty spiral staircase, but I'd have to second-guess where he might try to jump from the stairs.
The precariously-balanced wall-mounted bicycle, with its fascinating wheels that spin? Will the Nelson pendant lamp look like a tempting landing strip from above? How about that wall-mounted bookshelf, a few feet away?
It could be a DISASTER.

The more I look at that Ekstrem chair,
the more I think that it-- or something similar-- might make the ideal piece of cat gym equipment.
Maybe I could find just the right piece (or pieces) of cast-off tubular furniture, upholster the steel tubing with foam insulation, then cover with a finished sleeve of woven sisal. Voila, instant cat gym.