How about up in a tree? I always wanted a treehouse when I was a kid. Maybe I'll finally have one for my grandchildren to enjoy! The Pallet Project: Tree Hut, from pallets and skip treasure.
DIY Water Wall with recycled bottles
Jazzy Contemporary House in Minimalist Design: Awesome Modern Patio Design Minimalist Furniture Jackson House
Outdoor Play Area - pipes and tunnels
Fun with water, great recycled plastic bottle project. This could be pretty if you used wine bottles. It's just a matter of figuring out how to cut a hole in the side.