I've seen a boat hull made into a fabulous water garden:
grandkids-- I'd do a sandbox I'd submerge it about 1/2 way into the yard..
It could be a giant planter! Although I love the water garden idea too!
Stand it up on the transom (back end) and put shelves in it. Use for whatever you want; potted plants, books, etc. The possibilities are endless.
Pintrest has many ideas...