What is the fattest key to break through Beishan in the dark area?

Beicun folk house is located at the easternmost end of Beishan map. The Beishan Hotel, which breaks through the dark area, must take the key to enlarge the map. The key room is between the hilltop cabin and the grocery store, and its appearance is similar to that of the checkpoint cabin.

The ultimate goal of the game "Breaking through the Dark Zone" is to evacuate from the dark zone and collect materials and return home with full load. The booty brought out can be stored in the warehouse and sold for game currency.