This second passage's hatch led down to this strange vaulted chamber. There were no charred remnants, and there was a channel cut into the floor all the way around it at the base of the walls, and though you can't see it in this photo, the room sloped downwards from the entrance. Weird.
Beneath the entry ladder was a round tunnel just like the one in the smoker. I imagine at one point both tunnels met up, beneath the floor of the vehicle bay.
This photo is taken from the far end of the room, towards the tunnel and entry ladder bottom. If you look closely you can see my late trubbamaking companion's foot as he ascends the ladder.
At this point, we climbed back out of the first vehicle bay and prowled the woods until we found a second larger and more overgrown one. We were able to climb down into this second one directly on the thick ivy, and began to make our way through the vegetation looking for more passage entrances.