My wife, and I are in the initial stages of planning to build our own underground root cellar on our farm, to be able to store supplies long term. It would keep things at a constant 53* during the Summer, or Winter. This would pair well with the 16x10 greenhouse that I built during the Covid 19 shutdown last Spring.
https://www.instructables.com/DIY-GreenHouse-Build-Solid-Structure/