There are few things I like more than an easy, free project. This qualifies.
My backyard has quite a slope to it and a couple of different levels. It also has chunks of granite strewn about.
Chunks of granite + changes in elevation + a little work with a pick + a bit of carrying and stacking = a decent-looking retaining wall. The original idea was to build a raised bed planter there (which would have been less easy and free), but it doesn't get enough sun.
Best part? It has the Gus Sleep Spot Seal of Approval!