Whittier, Alaska, has a front door with opening hours. The only road in is a single-lane tunnel two and a half miles long through a mountain, shared with the railway, and it takes turns: cars one way, then cars the other way, then a train, and at night it shuts. Most of the town’s couple of hundred people live in one fourteen-storey building, with the post office downstairs and a passage through to the school, so on a winter night the whole town is home, the door is locked, and the place is less a town than a household.