It is a strange feeling that got hold of you after you fell through the portal... it was dark for a while, you couldn't say how long, and then there was the sensation of falling. Something was there, you could feel it all around you, a presence. There were whispers, so muted you couldn't make out words, but somehow, you shuddered nonetheless, and not from the cold surrounding you alone.
Then you awoke.
***
It is still dark, but something changed. There is a stone floor beneath your feet, and the air is warm and stuffy. Other people are here, dozens, you can hear them, breathing, moving against floors and walls, from time to time a heavy metallic jingle. No one is speaking a word, but you can hear a woman sobbing quietly some distance away.
Darkvision:
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The room is wider than you can see in the complete darkness, with massive stone walls. It seems that there are at least three dozen people here, all but a handful of them wearing the same brown, ankle-long shirt, half of them chained to the walls. You can't make out a door, only a metal trapdoor in the ceiling.