The southeast quadrant of Neverwinter is where a huge chasm opened during the cataclysm, a chasm which has been disgorging a constant stream of mutant monsters ever since. As if that wasn’t enough, staying near the rift for too long also makes people go mad. The other quadrants of the city only survive because they managed to isolate themselves from this one somehow.

The Ruined City

This isn’t a “bad part of town” like the River District. There’s nothing “town-like” about this expanse of ruined buildings and twisted streets. By setting foot in here you’re already on a proper dungeon delve. No one does this much any more, since few who try ever return and those who do come back changed.

PCs might be hired to search for someone who vanished here. Or they might end up sleepwalking here due to the Chasm’s influence and need to fight their way out. If they have a Spellscarred Harbinger, that character is going to feel an odd connection to the Chasm and a desire to explore it.

As we already learned from the faction descriptions, the Chasm goes all the way down to the Underdark, where it opens on an underground lake whose bottom houses a Spellplague pocket and the AbSov research base built around it. The Plaguechanged monsters are projects and rejects created by the aboleths - they have been growing more powerful and “efficient” as of late, as the creatures improve their designs.

Even if no other reason draws the characters to explore the Chasm region, they will eventually have to come here in a campaign where the AbSov is the greatest threat. Getting to them requires not only traversing the ruined city on the surface, but also going down the Chasm itself.

The Upper Reach

When descending the Chasm, the first few hundred feet might seem fairly mundane, but after that the landscape starts resembling the Elemental Chaos or Abyss more and more. Elemental energies surge up from the depths at irregular intervals. The walls are harder to climb, with handholds appearing and vanishing at random and occasional blasts of fire or wind erupting from them. Earthmotes abound, some drifting slowly and others bashing against the walls.

Monsters can be found climbing the walls or flying from the depths. Even those who have no flying ability can be seen floating up in bolts of chaos magic, particularly if they were sent to attack the surface.

Creeping Madness

At this point the Spellplague radiation is already so intense that characters are already at risk of contracting Creeping Madness, a magical disease similar to the plague itself. They must make a DC 10 Endurance check on every short or long rest to avoid contracting it. Further resistance rolls also use Endurance, with a Maintain DC of 10 and an Improve DC of 15.

Stage 1 inflicts a -2 penalty to Will and Initiative, and a +1 bonus to psychic attacks. Stage 2 eats a healing surge and inflicts -4 to Perception and Insight. Stage 3 inflicts a -2 penalty to all skill checks, and makes the victim’s attacks deal +1d6 psychic damage. Stage 4 drives you mad and makes you permanently dazed.

Unlike most diseases I think it’s possible to recover from the final stage through Endurance rolls. If a character fully recovers from stage 3 or later, they also gain a spellscar. The Spellscarred Harbinger has a +2 on all Endurance checks against this disease.

The Twisted Fane

This is the apparent bottom of the chasm, a broken wasteland whose rock pulses as if it was alive. There’s an alien-looking black fortress here, the Twisted Fane, which is built around an eerily shining crystal. The Fane is guarded by a colony of fouslpawn which will fight to repel any intruders they detect. The monsters attack on sight and fight to the death.

All of this is a ruse put in place by the Aboleths to stall any would-be heroes. They expect these interlopers to slay the disposable foulspawn, destroy the useless crystal, and go back home thinking they solved the problem of the Chasm. PCs can make several different skill tests to notice the crystal doesn’t have any actual power, the foulspawn are acting strangely because of mental domination, and that there are tunnels hidden in the area around the fortress, leading deeper underground.

Plaguechanged Warrens

This is an enormous chunk of rock wedged between the two walls of the Chasm. It could be moved by sufficient force, but only has room to go up. The top surface is where the Twisted Fane was built, and the inside is a maze of twisty passages that end in gross “breeding pits” where creatures are stuffed into fleshy cocoons and mutated by Spellplague magic directed by the Symphony of Madness. This is where all the plaguechanged monsters that attack the surface come from.

This deep into the chasm, characters have a -2 penalty to Endurance to resist creeping madness. At the bottom levels of the rock, they also start to hear the physical sounds of the Symphony of Madness, which inflicts a -2 penalty to Will on all non-aberrant creatures.

The Blue Cauldron

The underside of the Warrens opens into a large cavern mostly filled by an underground lake. The water glows blue and bubbles as if boiling due to the Spellplague pocket at the bottom.

There is no physical way to safely climb down to the water; characters must either fly or fall down the 60-foot drop. There is an “unfettered travel” magical effect put in place by the aboleths that lets them swim in the air inside this cave. Characters trained in Arcana might be able to hijack that and be able to swim through the air as if it was water.

At a depth of 20 feet, the PCs can find bubbles holding particularly interesting prisoners. At the bottom of the lake, is the research lab itself. Any characters who get to this cave will immediately draw the attention of the aboleths, both because they proved themselves a major threat and because they might make excellent research subjects. The aboleths themselves are quite powerful and might also be plaguechanged.

At this depth, characters have a -4 penalty to resist creeping madness.

Impressions

The surface of the Chasm could make for a decent hex- or point-crawling map as characters try to find a safe path to the rift itself. As described, it seems the Chasm itself is a very meaty dungeon delve. None of its separate areas described above get maps, so the GM can make maps that suit their purposes.

Sure, once you’re here you know you need to go down, but depending on how long the GM wants you to spend inside each of the named areas could vary in complexity from the equivalent of a single “room” with a big battle in it to an entire labyrinthine dungeon level where finding the way down is a significant challenge in itself.