Describe the bunker in the novel, Virals?

The main room of the bunker is about fifteen by thirty with walls of wooden beams rising to the ceiling ten feet high. A slit of a window gives a view of the Charleston Harbor and runs the entire length of the wall opposite the entrance. From outside, a wooden overhang keeps it from being seen. The second room which is to the left of the first one and can only be accessed through a passageway that is quite low. Beyond that is a shaft, partially collapsed, that runs deeper into the hill, but is not used.