You don’t know what Lord Bartoz nor the mysterious Tribunal want with the Seals of Astaroth but you're sure their intentions can't be good, so you've decided to thwart these sinister forces by finding the seals first.
You're making your way to the "nasty pits" where you know Bartoz's work crews are also searching. This is a section of Iskandar's sewer system even the Rat Catcher's Guild don't enter. Still, Tilma is in her element here, and Berry's temporarily enhanced vision certainly helps a lot, as does the borrowed driftglobe, which casts an eerie light on the slimy stone walls.
The sluice gates in this area stopped working generations ago. The effluvium that finds its way here doesn't join the rest of the waste water that drains into the bay. The stuff in the cesspools is old, stagnant, and disgusting. Real nasty.
Berry heard the man say "two levels down" but that's misleading. According to Squiddly's map, first it's a spiral staircase 30 feet down, then southeast a quarter mile through a maze of chambers, and then a precarious descent on metal rungs set in a 60-foot vertical shaft.

You've just cleared the spiral staircase. The air stinks but the canaries seem okay.
You head southeast. An iron gate that would've been an obstacle to anyone bigger than Squiddly or Berry looks like it's been forced open by the work crews. The first few chambers are a mess of rusted pipes leaking foul water that pools on the floor. There appears to be some recent damage to some of the pipes and stonework because of the quake. As you pick your way past some of these, another tremor rocks the chamber, bursting one of the pipes, dumping brown sludge which you narrowly avoid. The tremor passes, but more may come.
You come across some major damage, probably caused by the main quake. Part of the chamber is caved in, and half the floor has collapsed into a rubble-filled hole. It looks like the work crews built a makeshift bridge—not much more than a couple of wood planks—over the gap, but the aftershock has partially collapsed it. The near end of the bridge has fallen into the hole and then jammed against the rocks about 10 below you. The chasm is small enough that an athletic person could make the jump, but clearly not the safest route. What do you do?