Add cap blocks to the top row of a block or stone retaining wall. You can add a layer of masonry adhesive to hold them in place, then back fill. Or you can backfill as you go, then add the cap. Either (Patio Step Retaining Wall)
All you need are a few - pavers, landscape-block adhesive, and a little time. Wait 24 hours for everything to cure and youre ready to move your new planters into place and fill them with dirt and greenery.
I came into a dead end canyon blocked by a beautiful waterfall. I learned that even the most impassable path can lead to a beautiful ending.