Mine really like any type of tunnel. Chewable ones like cardboard, willow or hyacinth that will have randomly dissappeared within a few weeks or just plastic-y ones that get ruined within a few weeks as well.
They also like the chewable balls (willow balls, hyacinth balls, rope balls…) or anything not shaped like a ball that’s chewable.
I had a flower decoration piece hanging from their pen. It was on the outside but they kept pulling little flowers off it through the pen. So now I bought their own flower bouquet. xD I linked it below. Note, they are links to the brand Rosewood so not an actual webshop, as I’m not 100% sure that’s allowed. If you find something you like you can google the name of the item and it will pop up on 1000 webshops.
Here are some of my (and my bunnies’) favourite toys:
https://www.rosewoodpet.com/small-animal/activity-toys/boredom-breaker-corn-loofa-seagrass-sisal-toys/wacky-wobblers
https://www.rosewoodpet.com/small-animal/activity-toys/boredom-breaker-corn-loofa-seagrass-sisal-toys/floral-hanging-basket
https://www.rosewoodpet.com/small-animal/activity-toys/boredom-breaker-corn-loofa-seagrass-sisal-toys/corn-rattle-rollers
https://www.rosewoodpet.com/small-animal/activity-toys/naturals-toys-beds/trio-of-fun-ball-medium
And tunnel:
https://www.rosewoodpet.com/small-animal/activity-toys/naturals-toys-beds/hyacinth-tunnel
If you want a durable tunnel, don’t get a flimsy plasticy one you can fold up. Those are broken very fast, which is not a bad thing if they’re cheap but if they’re a staple to your pen (the only way to get from point a to b) you will want something sturdier. The chewable ones may be gone within a week, so take that into account as well.