Ok, Rah, Takuan and Wraith, going left and right, have foundf the support areas. There are rooms, an armoury (empty), a medical centre, and thung corridors that lead back into the rock of the valley and link up with the entrances to the gun emplacements outside. They are all still powered. There are some smaller corridors, on each end, that lead north and seem to slope downwards.
Galder, you have come out into a fabulously huge great hall. Done out in brown stone, it is several hundred feet high. Halfway up appears to be some form of control deck, from what you can tell from down here. And all the way up the top, not easy to access, is a smaller control area.