OOC III
12 miles of underground tunnels is easily a full days' travel. I've no experience with caving (more properly, spelunking, I guess) but if I imagine a good, solid hike through rough terrain expecting a distance of 12 miles in one day sounds about right to me. Perhaps two days' worth of travel if we took it a bit easy and/or encountered problems.
Heldig fancies himself a bit of a tactician (nothing that has a game effect at all, just a role playing quirk via a personality trait). So if we sit down to hash out a plan, he'd likely have some input.