The grey elf worked his magic, and the stone began to glow...and then it vanished!

Ged: (waves Lightbringer about, staring downward)
Belphanior: (steps back a bit) Get that thing out of my face.
Lightbringer: I resent that remark.
Belphanior: (ignores the morningstar)
Mongo: We should signal the others...get them moving in behind us. (he looks up) Above us. Whatever.
Alindyar: (floats upward) I shall handle it.

As the dark elf ascended, the remaining three descended once more.

Ged: We need a lantern.
Mongo: Its oil would spill out if you aimed it downward.
Ged: A magical lantern...or a spell.
Belphanior: (opens a tightly-sealed black pouch, from which a bright glow emanates) Not to fear. (he produces a small rock which glows with fiery white light)
Ged: Ah, the old continual-light-on-a-rock trick, eh?
Belphanior: Hey, I don't have to waste a spell this way.
Mongo: (covering his eyes) What are you gonna do with that thing?
Belphanior: Drop it...
Ged: Hmm...on second thought, is that wise? Anything down there would be alerted to our presence.
Belphanior: Anything down there already knows that we're up here. Besides, I'd rather see my foes ahead of time than drop into an unknown darkness.
Ged: (nodding now) Yea.
Mongo: Go for it.
Belphanior: (lets the glowing rock go, and it falls, fading as it goes...and then hitting bottom)
Belphanior: (listening intently) It didn't fall too far. The bottom of the shaft is pretty close.
Ged: Let's get down there.

As they descended again, they noticed that the surface of the shaft had changed, distinctly, after the point where it had been blocked by stone. Before, the shaft had been smooth metal, with a clean, polished appearance. Now, the walls of the vertical passageway glistened with a clear slime, which for some reason didn't run down but instead remained in place on the walls. As they neared the glowing stone and the bottom, they noticed that weird, ridged tendrils twined back and forth amidst the goo. These tendrils, or whatever they were, looked like living, bony spines, though they were cold to the touch.

Mongo: And slimy. (he wipes his fingers on his pants)
Ged: You know what this reminds me of? The Underdark.
Belphanior: (nods) That central tunnel that we marched through most of the time did resemble this...but not totally.
Mongo: You're right about that - this is even weirder.

As bizarre as the lower portion of the shaft was, the area at its bottom was a whole different world. The walls here weren't angular or smooth at all, but rather curved and spiny, run through with strange ridges of a dark, chitinous substance. They resembled bones in a way, though they were distorted into decisively non-human shapes and patterns. Various parts of this vaguely skeletal framework were coated in clear slime, like that on the shaft's walls. This chamber was roughly hemispherical, and about thirty feet across; it opened directly into another, much larger space, a rounded and ridged tunnel of enormous size.
This next chamber was easily two hundred feet across, and its walls were essentially a larger version of the bizarre formations found in the previous area. The air here was cool and dry, quite a bit lower in temperature than that found above the point where the shaft had been blocked. A fine blue mist covered portions of the huge tunnel's floor - a floor which was solid, though irregular due to the ridges which jutted out all along its length. Even the slightest sound seemed to echo forever in this mammoth place, and the glow cast by Lightbringer suddenly didn't seem so bright.
The cavernous passage extended out of sight in both directions, curving away, cloaked in darkness.

Ged: Boccob!
Mongo: Tomb, my ass. This is something else.
Ged: Yea...
Belphanior: (looking around) I still don't detect any souls around us.
Ged: Don't be offended when I tell you that that doesn't reassure me in the least.

They heard noises behind them, but it was only their companions, who had descended the shaft and were now filtering through the archway and into the gigantic chamber.

Bosco: (awestruck) We're like ants here.
Otto: If that's so, where's the ant-lion?