I have a fresh idea, perhaps. Considering interaction and freedom of player choices, there might be a way to add depth quite literally to places.
How about the player being able to craft a “mine shaft entrance”, which is a loaddoor for a new level.
The player will then be able to go inside, and keep mining stone and ore’s, and eventually use explosive orbs or wood & fire to extend the shaft deeper up to a maximum depth by x stages.
Each stage is a pre-produced shape that snaps together.
The Mines could have different themes depending on the environment: high plateau: rock, lower redwoods: dirt and so forth.
Now, whenever a new part of the mine is opened by fire or explosion, and ceiling collides, you have to move things out (you could consider a lorry and a horse but thats cosmetics and not necessary).
Behind, you could have good luck, and ore deposits await, or a small underground river, - or animal creatures like the bugs, or demonic creatures (the deeper you get).
It could be a way to add gameplay value and ambushes with creatures as well as resources and make use of building and interaction gameplay. Maybe it also fits nicely for one or the other player roleplaying and building a nice castle.
I know, its very blank at this level, but combined with some of your dungeon ideas or mechanics, maybe it is a useful concept?