Back in the eerie Underdark, they travel a few days and reach a fork in the road they previously skipped and see another giant mechanical spider. They kill it and wrench free another crystal eye.
After a couple of days traveling down the narrowing path, they happen on a large, smooth metallic door, with lots of tiny inscriptions. It reacts to the cube and opens.
Inside, they find smooth metallic walls and floor. Weird webbing covers the ceiling and corners, and debris and evidence of centuries of decay litter the room. Among them is a tall smooth piece of furniture with a black glass window facing them. When they approach, it lights up from within a pale green light, and glyphs of old common appear. It gives them a series of numbers, and begs a response…
They find a set of buttons on another device and enter what they think is the response. It worked. A door opens.
On and on for hours they search and find more devices, open more doors, and fight great quadrupedal humanoid mechanisms that shoot fiery beams from their eyes, and giant pink brains with dangling tentacles. They eventually happen upon a large crystalline dome inset with lots of copper tubes and wires and inscribed upon it says “only the blood of the faithful servant shall provide passage.” They notice a large black rope attached to the dome, and one end of the rope dangles off a cliff. Across the gap, they see the other end, frayed and sparking with lightning-like energy.
They manage to find a safe passage to the other side of the gap, and with the use of ropes, ladders, and a bit of luck, they connect the two ends of rope. The dome of crystal and copper glows.
Barlo opens a vein on his arm, and a drop of blood hits the dome.... they see Barlo consumed in flame, his body turned to ash.
One by one, the rest of the party are consumed.