I have 2 cats and as in the other reviews, they just kind of explored the tree for a couple days, never lingering on it for long.  At one week, they were on it alot, and now at 2 weeks, they are always on it.  Either sleeping in the box, on all of the upper levels or swatting at each other from different levels.  My youngest cat (3 yrs) climbs up the side like it's a tree, from bottom to top. And I was surprised to see that they both use the ladder and play more with each other on those two levels.  My main coon (11 yrs)  is heavier but still will squeeze herself through the opening at the top of the ladder.  My son and I enjoy watching them play.  Very entertaining.