After completing the quest "A Matter of Myrmidons", speak with Barnaby again and choose "Hear More" from the dialog options. There will be a cinematic. Barnaby leads you towards a gate. He tells you that beyond the gate, lies the Everfall, an ancient place that sleeps beneath Gran Soren's stones. We pawns have long served as keepers of the entrance to this place. But since the dragon's coming, a strange aura has filled the Everfall. A presence. If it is some omen of evil to come, we cannot allow it to go unchecked.

Barnaby asks that you seek out the cause of the change, or some proof of what's happened. The Everfall is a place unique onto itself. This is not a simple task, nor a favor he asks lightly. The quest begins:

Lure of the Abyss
Explore the Everfall

Go through the gate and enter the Everfall. Explore this area. Enemies here include Bats, Undead, Skeletons, Spiders, Harpies and more. You will also find some loot and treasure scattered around, such as a chest with a large coin pouch. There are also giant coin pouches with even more gold to be found in the area. If you are having difficulties with all the monsters that spawn in the Everfall, you can just cut the exploring to a minimum and make your way straight towards the bottom.

There are many undead and skeletons inside the Everfall, and they will spawn in may of the areas. But the main thread you encounter is an Ogre. This is a giant monster that deals a lot of damage with every hit. It hungers for humans, women, most of all. So if you have female pawns and you are male, the Ogre will focus on them first, which gives you some breathing room. You could also lure the Ogre to the cliff/abyss nearby, and if you can make it fall off, it will die.

Keep working your way down.  You will arrive at a flight of stairs going down, then up. There is a lever that opens the gates. Eventually you reach an area called "Ceremonial Cage". Check the coffins for loot such as Flammica, but watch from additional skeletons that come out of the coffins. Pull an engraved lever to go through another gate and into a treasure room. Grab the items you want, then retrace your way down the stairs, but turn left into the tunnel. You arrive an a zone called "Flameservant's Throne". Examine the circle in the center. The floor gives off a curious light, and a draft. Something lies below.

Suddenly a lot of worm like monsters spawn. Your quest goal updates, to report to Barnaby. You should not fight these worms, there are too many of them and more and more keep growing back. Instead you should just go back up and exit the Everfall. Climb the spiral staris, and to the second floor. Order your pawns to come with you. Use the levers to unlock any gates that are blocking your path. A cutscene soon triggers where you escape the Everfall.

Talk to Barnaby (Blue Question Mark above his head). You report what you saw, and about the light you saw from the floor.

This completes the quest, Lure of the Abyss