You could do like a forest theme, if you really really wanted to you could make it bioactive. I know there is a lot of enrichment that comes with that option but you would have to look in to it a lot more if you were even interested.
Haha! Funny you say that, that was my last theme before the picnic one! Though, I might keep this theme for a little longer, because I have to schedule a vet appointment soon, and I don’t want to cause any problems with stress. But still suggest themes for when I do change his cage!!