We had talked about something like that. Would be nice if it was more convenient access than this would be. But it’s a solid idea for keeping things dry and cozy.
With a pickle barrel you don’t have to bury it all the way you can leave the top uncovered or even turn it on it’s side and cover it with dirt, leaves, straw or whatever just keep it wet to keep it cool.
Root cellars are good for fresh food storage but they are high in humidity so anything metal, like jar lids, will rust.
What are you trying to store?