Litter box cover from 2 IKEA side tables and fabric! This is a great DIY for cats, better than traditional covered boxes because it doesn't have plastic on the sides, which can trap odors and make some cats reluctant to use the box as often as they should.
Here's a sandbox with edges created from sections of logs. No need to have a rectangular shape. Even place a boulder along one edge or a stump for sitting on. This one provides both sun and shade. Cover with a tarp if you want to keep out cats.