I kinda like to 'ruinize' unused builds. I.e. add vines and let it overgrow, add leaves, yes break glass, add cracked stone etc. Wear it down a bit. And yes, the above suggestions can be incorporated into it (adding signs that explain, etc).
I wouldn't return the land to its old state. It's nice to see the history of the location. And you've prolly (branch) mined extensively underground, so travellers will know that this land has been used.