Hollowed Tree.

This large hollowed tree can fit many cats inside. It's important, because it's an amazing place to train apprentices. It could be raining and they wouldn't have to worry about a storm - well, the way the hollowed tree is tipping, it'd be dangerous if there was, let's say, a tornado but you have nothing to worry about. This makes this tree an ideal place to train. The branches stretch far up into the sky, as if they're holding it up. But, it blends in with the thick canopy, so you wouldn't be able to spot it if you were a bird.