Would it count if a mine was part of a bigger sub? I'm making something that keeps growing, see.
Whoops, sorry I missed this. Technically, anything with the freetext counts. Personally, my rule of thumb is this:
If I were looking for a mine (in this case) for a game, and I clicked on your sub, would it be useful to me? If so, it should have the freetext, otherwise it shouldn't. So, if you have some specific mine, or a monster that lives in mines, or some cataclysm that started in a mine, those would all be good. An NPC who is afraid of mines, or a book with a picture of a generic mine are probably less useful.