Locating a mine in a cave

[Raephire]

So how exactly do you begin building a mine shaft?

[Gaiadin]

when you are within a few % your prospect attempt will automatically walk your character to the point and open the build window. I'm not positive but I'm guessing if you don't have a wooden block available to hold the construction sign open, you will have to prospect again to reopen the build window when you do.

[Sarge]

when you are within a few % your prospect attempt will automatically walk your character to the point and open the build window. I'm not positive but I'm guessing if you don't have a wooden block available to hold the construction sign open, you will have to prospect again to reopen the build window when you do.

This

[SynthesisAlpha]

The mines should always be accessible. Of course, it's not as if there isn't even the remotest possibility of a bug in the map generator, but I haven't found any such situations in my ocular inspections of the generated maps, at least.

I've prospected a mine above ground that existed past the invisible barrier at the edge of the map grid.

[Sever]

If you stand near a ridge and select a cabin/mansion to put down (like you were going to place it for building) and cover yourself and the ridge with it, it shows the yellow outline like you see in that picture. I've located caves using that, and you can tell when it's a cave. Some of the ridge ends look strange like that, but it's definitely not a cave.