We bought an indoor tower for our cats. Don't get taken by a premium let chain store. We bought ours at an odd lots type store (Ollies). The cats like it we saved money.
Don't have cats . But my sisters husband made her 2 out of wood and heavy cardboard tube . Then wrapped it in natural rope and glued it on ( some nails to hold ends etc ). Was a great project and it was better and cheaper then store bought.
Yes the cats loved all the different levels and boxes .
i would think indoor carpeting on the walls ceiling and floors , cats like too scratch stuff and lots of round openings and short tunnels they can peek out of