The Road to Selt Lat

The party begins to explore an extensive and intricate cave system underneath Grimcatch, looking for a way down to Dol Gemen Lom.

They find the place mostly barren and deserted.  They track bare footprints through the dust for a while that seem to go nowhere, and in the empty echoing halls find the skulls of grimlocks, spiked to the walls with sharp iron stakes, and another skeleton spiked to the ground (and a potion and a gem nearby).  There are wide, maddeningly deep chasms crossed by rope bridges (which are at least in good repair), and a lot of twists and turns and dead ends in the rock.

They come upon a place where a tribe of primitive humanoids has made a home, but find that it is quite recently scoured by fire, and all the humanoids are dead, their paleolithic artifacts left where they lay and a pile of burned bodies off to one side of the cave.  (Mixed among those bodies, there are also the bodies of zombies, the less-recently dead.)  Near that, they find a very strange zombie with a wooden crate instead of a head.  This creature has had its arms and legs destroyed by the fire, and it strikes itself in the head repeatedly with its remaining arm stump.  Tiffy stabs it to death, and then pries the lid off the box but finds nothing but an infestation of spiders and some kind of recently-living internal organ on top of its neck.
After a bit of investigation, they discover that the box is some kind of spell container.  Written on its front, in infernal, is the word "Purge".  On the inside they find the spell summon swarm (spiders).

Deeper still into the caves, the party finds another chasm and another bridge.  This time they spot a bunch of the zombies standing near a lit torch.  They start to move toward the heroes, but Maurice cows them with a powerful rebuke, and only a few are left to attack.  Tiffy and Ellira begin to spray them with lightning, but this has an odd effect; spells seem to go off randomly every time one of the zombies loses its head.  When the party finally manages to immobilize all the zombies with webs and rebukes, one ill-timed lightning bolt splits open a crate that causes a powerful fireball, which consumes several more zombies, causing lightning bolts to fire back at the party, a magic mouth to start screaming, and other strange effects.  Ellira ends the threat of the remaining zombies by magically warping the bridge to drop them into the void, and the party continues on.

Finally, they arrive at Selt Lat.  This appears to be some kind of underground haven for monstrous humanoids.