My kitties knock them over all the time! We are planning to put them on a wider base or connect them together to make them a little more stable. I think we got them at Wal-Mart for $12.99 or so.
I had one of those when this was a two cat household. Midnight thought it was great fun to tip it over at night and roll it through the living room. It makes a very distinctive sound, one that wakes you up very quickly! roll-roll-roll-roll-roll...
We bought just one cubby hole for Spooky when we brought her home. We wanted something only she could squeeze into. Shelly can get in there - but just barely! He still tries to squeeze in there, LOL! Guess we should have gotten this model!
I have two of those. my boys are too big. We got them one of the really really BIG kitty condos. I bet the little kittens are going to loves those when they get alittle bigger!