Return to Undermountain
Room 23: Cavern, Part 2 (EL 12 and 13)
By Matthew Sernett

Area A

Area B

Area C

Prevailing Cavern Summary

Creatures: (Many) See area descriptions and the Other Cavern Inhabitants sidebar.
Traps: None.
Terrain: Cavern Floor: DC 10 Balance check to charge or run.
Cavern Ceiling: DC 25 Climb check and DC increases by +5 if surface is slippery.
Cavern Wall: Hit points vary based on thickness (hardness 8), Climb DC 20.
Fungus Forest Squares (see map): Costs 2 squares of movement to enter this difficult terrain.
Lighting Conditions: Darkness and shadowy illumination (mushrooms, fire beetles, will-o'-wisps).
Magic: None.
Detectable Alignments: See area descriptions.
Secrets: None.
Treasure: None.

The Map

The map for these areas are available in two different sizes: One serves as a reference for the DM, and the other is a map with a grid that works nicely with your miniatures.

Each map is presented as a compressed (zipped) Adobe Portable Document Format file (pdf). You need to have Adobe Reader installed to use it. Adobe Reader can be downloaded for free from the Adobe website.

Room Location on the Poster Map: This room is on pieces 7 and 8 of the poster map. You can see the pieces in thumbnail size in the introduction to this series. For a better idea of where this room is, please view the Article Reference Map.

Area A Summary

Creatures: None except nearby shriekers and giant fire beetles.
Traps: None.
Terrain: As prevailing cavern.
Lighting Conditions: Shadowy illumination (fire beetles).
Magic: None.
Detectable Alignments: None.
Secrets: None.
Treasure: None.

Area A Relevant Checks

Heal DC 10: This result allows a PC to determine that the roper died from slashing and burning wounds.

Heal DC 15: This result grants the following information and that from lower DCs: It looks like claws and teeth killed this roper. It's missing its gizzard but not many of its other internal organs.

Heal DC 20: This result grants the following information and that from lower DCs: The burn wounds seem to have been made by electricity.

Spot DC 20: A PCwho can see the fungus forest to the northeast and succeeds at a Spot check to this degree notices that creatures seem to be avoiding the cave past the far fungus forest by the pool.

Survival DC 15: A PC with the Track feat can determine that the roper fought a slowly moving battle as it walked from the northeast before dying here.

Area B Summary

Creatures: (1) One purple worm.
Traps: None.
Terrain: As prevailing cavern.
Lighting Conditions: Darkness.
Magic: None.
Detectable Alignments: None.
Secrets: None.
Treasure: None.

Area B Relevant Checks

Knowledge (arcana) DC 26: A PC that succeeds to this degree can identify the "boulders" as purple worm eggs.

Area C Summary

Creatures: (2) Two dread wraiths.
Traps: None.
Terrain: As prevailing cavern.
Lighting Conditions: Darkness.
Magic: None.
Detectable Alignments: Strong evil, strong law.
Secrets: None.
Treasure: None.

This article assumes the PCs enter the cave from the west side of the cavern. If they do not, modify the encounters to suit your needs. Level 1 Cavern, Part 2 describes most of what remains of the large cavern on level one of Undermountain. The article following this one will describe the other parts of the cavern and rooms that lie beyond. As the PCs enter each area, use the read-aloud text for that area.

This cave developed a strange ecosystem due to Halaster's husbandry. Small insects flit about or crawl on the ground, providing food for thousands of bats that periodically leave the cavern to fly about Undermountain before returning en masse. These bats create waste that helps to form earth in which the glowing mushrooms and other fungus grow. The cavern's fungus forest provides food for giant fire beetles, which in turn provide food for some of the cavern's other inhabitants. The monsters described in the area descriptions below exist largely outside this ecosystem, leaving the cavern to hunt for larger and better-tasting meals than fire beetles.

As the PCs explore the cavern, describe the features they encounter. The area descriptions below offer more details. If you'd like to have the PCs encounter creatures other than those listed in the area encounters, consider the monsters listed in the Other Cavern Inhabitants sidebar. The many small side caverns not given any particular detail in this article make good places to encounter such creatures in their lairs.

Fungus Forest: The map depicts several areas of fungus forest growth. These squares are difficult terrain. The large mushrooms block passage. They have a hardness of 6 and 480 hit points, and each is about 5 feet tall and 4 feet thick. These large blue mushrooms glow with a dim radiance and release a sparkling cloud of spores when disturbed. The spores are harmless. Several of the large mushrooms in the fungus forest are actually shriekers.

Chasm: The chasm roughly in the middle of the cave is 100 feet deep, and it grows narrower as one descends. Nothing of note lies at its bottom besides the bones of creatures unfortunate enough to fall within it.

Cliffs: The southern part of this side of the cavern rises in steplike cliffs. Each cliff is roughly 15 feet high. The ceiling ascends with the floor but with a more gradual slope. The cliff walls have a Climb DC of 20.

Other Cavern Inhabitants

A number of other creatures might inhabit the cavern, and the PCs could encounter them while exploring, resting, or during a fight with another creature. The following creatures are of a CR too low to be very threatening to PCs of a level appropriate to the challenge of facing the encounters in the area descriptions, but they might be interesting as noncombat encounters or as easier breaks between big fights. Also, one of these creatures could be quite challenging for a lone PC or one on the edge of a fight that has the other PCs occupied. You might also consider having multiples of these monsters confront the PCs, thus raising the difficulty of the encounter.

  • Average Xorn: CR 6; Monster Manual page 260 and Underdark 28/60.
  • Bat Swarm: CR 2; Monster Manual page 237.
  • Carrion Crawler: CR 4; Monster Manual page 30 and Dragoneye 41/60.
  • Choker: CR 2; Monster Manual page 34 and Aberrations 47/60.
  • Delver: CR 9; Monster Manual page 37.
  • Dire Bat: CR 2; Monster Manual page 62 and Underdark 44/60.
  • Phantom Fungus: CR 3; Monster Manual page 207.
  • Ochre Jelly: CR 5; Monster Manual page 202
  • Umber Hulk: CR 9; Monster Manual page 248 and Harbinger 44/60.
  • Violet Fungus: CR 3; Monster Manual page 113.

Area A: Dead Roper (EL --)

Read or paraphrase the following text when the PCs come within 60 feet of the roper's corpse.

The normal scents of the cavern are suddenly overtaken by the stench of death. Somewhere nearby lies a rotting corpse.

Read or paraphrase the following text aloud when the PCs see the roper's corpse.

As you approach the forest of mushrooms, a glowing mass of a dozen giant fire beetles scurry away from what they were feeding on, revealing an enormous heap of rotting flesh. It looks like a roper. Many of the nearby mushrooms have been crushed, and a few of the larger ones look scorched.

The roper from Room 21: Moving Day lived in this part of the cavern. The dead roper is a sibling that lived in the narrower caverns to the east. When new residents moved into those caverns, they chased out this roper and killed it. The roper from Room 21 heard the moving battle and fled, leaving its sibling to be killed.

The giant fire beetles have made little progress in eating the roper's tough hide besides worrying those wounds the roper suffered in the battle. If the PCs examine the corpse, a Heal check reveals some clues about how it died.

Area B: Purple Worm Lair (EL 12)

When the PCs approach this area, read or paraphrase the following.

The hard bedrock of the cave gradually gives way to hard-packed earth and gravel. The walls still seem solid. Perhaps these caves run closer to the surface than other parts.

When the PCs spot a purple worm egg, read or paraphrase the following.

A dark ovoid sits nestled against the wall. It looks much like a large boulder, but its shape is too regular to be a natural stone. A thin and drying layer of slime coats the whole rock.

The ovoid mentioned in the read-aloud text is one of many purple worm eggs in this chamber. A purple worm in the process of laying its eggs has picked this room as a nursery. Currently resting after a spate of egg laying, the purple worm lies beyond the stone walls of the cave. If the PCs approach within 40 feet of the pool, the purple worm detects them with its tremorsense and burrows up to burst from the pool in a shower of chilling water.

Purple Worm Eggs (8): Each egg is about 5 feet around and has a hardness of 8 and 50 hp. If the PCs don't destroy them, the eggs hatch in three days. Once hatched, the young purple worms immediately start burrowing in search of food. If you'd like to have the PCs fight the young purple worms, use the statistics for a giant constrictor snake.

Purple Worm (1): Use the statistics from the Monster Manual. The purple worm attacks until all the PCs are dead or all its eggs are destroyed. Note that the purple worm can burrow on this level of the cavern but other levels have hard bedrock that it cannot dig through.

Area C: Drow Ruins (EL 13)

When the PCs approach this area, read or paraphrase the following.

Ahead you see walls and an archway built into the cavern wall. The slim spires of stone, black rock, and spider motifs leave little doubt about who built the walls of the structure, but the drow must have left long ago. Broken bits of masonry clutter the ground near the walls, and there's no sign of a door even though the archway was clearly built to hold one.

When the PCs move to within 5 feet of one of the doorways, read or paraphrase the following.

The cave seems to grow colder here. As you peer through the archway into the room beyond, you get the sense that the chill is emanating from within the dark place.

This ruin used to be part of a drow outpost in this cavern. The nature of the structure and the purpose of the individual rooms can't now be determined. The place was looted long ago.

The spirits of two drow remain here. Halaster killed these drow, a cleric and a wizard respectively, in a terrible battle that lasted hours. Infuriated by their tenacity, Halaster trapped their souls here as wraiths. Over hundreds of years, they have grown powerful -- if a bit crazed. Now dread wraiths, these undead lurk in the walls and wait for the PCs to reach the center of the ruin. Then the dread wraiths attack, one on each side.

Dread Wraith (2): Use the statistics from the Monster Manual. The dread wraiths attack until all the PCs are dead or until they leave the ruin. The dread wraiths cannot leave the ruin, but they can hide within the stone walls, floor, and ceiling so long as they don't move more than 10 feet into each area.

Adventure Hooks and Tie-Ins

  • If your PCs have too few levels to face the threats described in the area descriptions, consider having them face some of the monsters in the Other Cavern Inhabitants sidebar in those areas instead.

  • The drow ruins could offer more adventure and exploration potential if you decide what the ancient building's purpose was originally. Perhaps it was a place for magic experiments, kept far away from the rest of the drow settlement in Undermountain and located in this cave so that long-range or large spells could be tested without fear of wounding other drow. The ruins might hide an ancient portal or even spells developed by the drow.

  • Drow ruins stand in this side of the cavern and duergar ruins stand in the other. Perhaps somewhere in this cavern lie the hidden remains of an ancient battle between the two.

  • Use the interesting side caverns to create your own encounters.

Check out the Return to Undermountain: An Introduction for more details.

Article Reference Map

About the Author

Once Editor-in-Chief of Dragon magazine and now a game designer at Wizards of the Coast, Matthew Sernett wrote in a Dragon editorial that there's nothing in D&D he likes better than when the adventurers flee through the dungeon, running pell-mell through traps and past monsters because what chases them is worse. When he wrote that, Matthew was thinking about Undermountain.


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