I just started Wintermute, and already I can see that there really needs to be an airstrip on the island. Will and Astrid planned on landing somewhere. I would imagine it should be near Milton as that seems to be the central community of this island. There could be a route out of Milton to maybe a coastal port similar to DP, where instead of a whaling station we have a ferry or cargo dock, but is too rugged to be an actual community like Milton. Maybe have all the major transport routes meet there, with railways near the shore to unload onto boats, and a truck stop for the loggers, with the airstrip for cargo and crew transport. Lots of oil and logging industries in the far north use fly-in/fly-out crew rotations for remote areas where vehicle travel is unreliable.
I haven't gotten far enough into Wintermute to find this prison bus I've seen mentioned. It seems unlikely that such a sparsely populated island, no matter how isolated, would have their own penitentiary. Closest thing that might be is an RCMP depot with a few holding cells. It's likely the prison bus was a mainland transport collecting inmates.
This would be a wild trip, I think. Sure there could be open areas to allow daylight in on occasion, but for the most part you're either stumbling around in the dark or chaining torches, hoping you don't run out. The only problem with a map like this would be finding a purpose for it, beyond the desire to explore. There would have to be something specific that would be valuable draw, like renewable coal areas (maybe occasional tremors bring more coal down, like storms do for sticks and branches) and/or a new resource like ore, which could be used like scrap metal but is also renewable (again with tremors.) Maybe having the cave come off FM so there's a forge nearby, but in hostile territory. Then having an area that provides you unlimited coal and metal might be worth the risk of roaming an area in total darkness.