OOC:
Ok, waiting for the books to have completed burning will color the timeline a little differently.
And yea, we can handle stealth as a group check here, which just requires that at least half the party succeed. And two of you rolled well!
Moving slowly and quietly, you reach the top of the stair and find that you're all looking in on a large hallway with what-appear-to-be cells, like for imprisonment, lining one side of it.
Though the bars and doors are mostly long ago corroded and fallen to the ground.
At the far end of the wide hallway, you see a person peering into one of the cells, they're holding up a torch and literally-sniffing about - likely searching for the source of the faint smell of smoke.
There is another stairwell at the far end of the hall going up, beyond the person peering in the cell, and if they came from there; then there is one cell they've already searched behind them and three more ahead. And then your stair. They're likely moving your way...
They have a torch in one hand, and what looks like a hand-axe in the other. If they're wearing armor, it is just padded or perhaps leather. They haven't noticed you yet.