Rabbit play pen. Ours used five 2x4's (cut in half length-wise). Then use one of those to make the uprights(two feet tall). (all boards become 2x2's) One roll of chicken wire will keep the bunnies in. Great for the kids to be able to play with the rabbit in the yard.
I tried this with my bunnies hutches with irrigation pipe and drilled holes in it to filter out the pees and poops. The rabbits absolutely love it! It's nice and dark and they just chill in there as they see it as a safe and spot.