Enrichment in cages

Hello! I am new to (meat) rabbit raising. I currently have a male and female (in separate kennels), and a week old litter of 7 on the ground. They are living in large kennels with concrete floors and wooden and fenced sides. They have straw for their bedding. The kennels have shelves built in, the lower one about a foot off the floor, and the higher one about four feet up. (The male manages to jump onto the higher shelf, which I find quite impressive.)

I would like to add more enrichment to their kennels, as quality of life is very important to me. I am familiar with enrichment for dogs and cats in the form of food toys, foraging activities, regular play toys, adding new smells and objects to explore, and (for cats) having lots of hiding and climbing places. I have no idea what is appropriate and enjoyable for a rabbit, though!

I tried giving them cardboard boxes with holes cut out for hiding places, but both the male and female would repeatedly flip the boxes over and then ignore them.

Any other enrichment ideas are greatly appreciated!

Mine seem to like their shelves and emptying their hay racks most of all. Toilet paper tubes stuffed with hay and hay cubes are pretty popular.

All mine have balls (whiffle balls that are light and can be picked up by the holes) and short chunks of pvc to play with, but I don't see them using them very much. The babies do like to lie inside the 3' pvc sometimes.

When I could find it for cheap, I would tie sea grass rope into big knots and hang it in the cages as a treat, one of those is typically gone in a half hour.

You can get bags of sliced and dried yucca root, they're meant to hang for parrots and if you break them in half they'll chew them. These get pretty expensive and don't last too long because they soak up pee and have to get thrown out.

I think they are pretty content little creatures. Whenever mine have a burst of play energy, they play on the shelves more often than with things. That said, they do get really excited for their handful of greens in the morning and slice of dried banana or raisin at night, but you can't overdo the candy

Another fun toy to make for them (mine seem to like them, at least), are scrap chunks of wood or short sections of a safe branch (apple is popular) and a little plastic ball with a bell inside, all hung together on a shower curtain ring. I attach mine to the side of the pen, and they like chewing the word and flinging the bell around.

Hello!
I love using pinecones for my bunnies! They're easy to find as well and free! I like to give them to him plain, or hang them up in the cage so they have to reach up to get them. It's also fun to make a rabbit-safe glue ( flour and water mixed together until a paste) and then drizzle it other the pinecone and sprinkles seeds or oats. once it's dry it will Harden and it will be fun for the bunnies to nibble at the oats and seeds. a good border breaker!
Cardboard boxes and cardboard in general seems to always be a winner with rabbits. Mine love the boxes and chew and toss them all around the place! They also seem to enjoy toilet paper rolls filled with hay.
Brown paper bags are always really good. you can fill em with hay and the bunnies will have to nibble their way to it!
Food works for everything. Tying up carrots and veg so they have to stretch to reach them is a very fun treat! it always works their teeth and keeps them in trim.
Plastic toys can be good as well as long as your bunnies don't chew them. Little balls that were meant for cats are fun to toss around. baby toys like the little keys or rattles are good as well.
Branches like someone mentioned earlier are really fun as well!
hope this helps!

Small empty cans and plastic pots get pushed and tossed around by my bunnies. They also put the smaller can into the bigger one.

Not seeing where you are but I sometimes use dried coconut husks. They like gnawing and flipping it. Also see them doing it with cardboard (the brown, corrugated type). Another member here use small coconuts that fall off the tree.

Thank you for all of these awesome ideas!! Can't wait to try them out.