Deep beneath the ancestral home of the Sarwin family, an ancient evil stirs in its slumber. While many D&D adventures revolve around stopping a ritual before it begins, The Thunder Below drops the players into a situation where the ritual is already halfway done, the castle has been breached, and the villains are tearing through the magical defenses. Written by James Jacobs, this epic D&D 3.5 adventure for 17th-level characters is a massive, multi-faction dungeon crawl with world-ending stakes.
Introduction: The Fall of Sarwin
Six hundred years ago, the legendary adventurers Annah and Zebulahr Sarwin defeated an orc cult attempting to awaken Ubothar, a colossal entity known as the “Thunder Below.” To ensure the creature remained asleep, they built Sarwin Castle directly over its prison, warding it with epic-level elemental magic.
Recently, the ghost of the ancient orc druid Tiboquoboc possessed the youngest Sarwin heir, Arezi. Using her body to bypass the initial wards, he slaughtered the family and invited his monstrous allies to invade. When the players arrive, the village of Sarwin is a smoldering ruin, and Tiboquoboc’s army is currently fighting a brutal war of attrition against the castle’s automated magical defenses to reach the vault below.
Narrative Core: A Dynamic Timeline
What sets The Thunder Below apart from standard dungeon crawls is its living timeline. The adventure doesn’t wait for the PCs. Tiboquoboc and his elite lieutenants—a coalition of harpies, blood fiends, and green dragons—are actively exploring the castle, disarming traps, and battling the elemental guardians.
- The Ticking Clock: The module tracks Tiboquoboc’s progress day by day. If the PCs delay or retreat to rest, the villains push further into the dungeon. By Day 5, Tiboquoboc breaches the final vault. By Day 6, Ubothar awakens, and the campaign is effectively over.
Tactical Breakdown: The Invading Army
The enemies in this adventure are incredibly diverse and powerful, forming a highly organized strike force.
1. The Orc Camp (Area B)
Outside the castle, the Ironmaw Orcs have set up a fortified camp. These aren’t standard low-level fodder; they are 12th-level Barbarians (CR 12). They are supported by the very old green dragon Alorzulan (CR 20), who provides aerial bombardment with his corrosive gas breath weapon.
2. The Skytower (Area 26-62)
The upper levels of the castle house the Sarwin family’s magical artifacts, including the Stasis Scepter and the Sky Key.
- The Guardians: These areas are defended by Advanced Elder Air Elementals (CR 17) and Greater Stone Golems.
- The Traps: The doors are forged from magically treated adamantine and rigged with Lightning Traps and Symbols of Insanity. Players must navigate these epic-level defenses while simultaneously racing against Tiboquoboc’s team, who are trying to loot the very same rooms.
3. The Villainous Lieutenants
Tiboquoboc’s inner circle is a nightmare to fight:
- Lzierabel (CR 17): An Aasimar Cleric/Thaumaturgist of Nerull who relies on Time Stop and quickened buffs to turn herself into a melee powerhouse. She is accompanied by her lover, Amiryll, a Succubus Assassin, and a Blood Fiend bodyguard.
- Muraxus (CR 17): An Aranea Rogue/Duelist who uses Spring Attack and Expeditious Retreat to harry the party while fighting defensively.
The Boss: Tiboquoboc (CR 25)
Tiboquoboc is a horrifying amalgamation of classes: an Orc Ghost Druid 6/Sorcerer 5/Geomancer 9.
- The Possession: For most of the adventure, he is possessing the body of Arezi Sarwin. If the players simply blast him with spells, they will kill the innocent girl he is trapped inside.
- The True Form: If forced out of Arezi’s body, his true ghostly form manifests. He attacks with a +2 ghost touch icy burst scimitar and utilizes his Pounce ability to shred spellcasters. As a Geomancer, he draws power from the surrounding terrain, casting spells at +2 caster level.
Mechanics & Hazards: The Pit of Ubothar
If Tiboquoboc breaches the lowest levels, he reaches the Pit of Ubothar (Area 84). The floor of this 500-foot-deep shaft is actually a single, colossal scale of the slumbering beast. The text advises DMs that if Ubothar awakens, its CR should be at least 28—suggesting stat blocks like a Colossal 30-headed Purple Worm or an exiled Demon Prince.
System Conversion: 3.5 to 5e and OSR
Running a CR 25 villain requires significant adaptation for modern systems.
For 5th Edition (5e):
- Tiboquoboc: Use the Lich stat block, but change his spell list to Druid spells and add the Ghost‘s Possession ability.
- Lzierabel: Use the Death Knight stat block but replace the martial weapons with cleric spellcasting.
- The Elemental Wards: Treat the adamantine doors as having an incredibly high AC (22+) and immunity to all damage below a certain threshold to replicate 3.5’s hardness rules.
For OSR Systems:
- OSR games rarely reach this power level. This module is best used as a framework for a massive, multi-faction siege where the players must manipulate the castle’s traps to destroy the invading army rather than fighting them head-on.
GM Tips: Managing the Chaos
- Track the Timeline: The daily schedule is the heart of the module. Let the players find evidence of the villains’ progress—smashed golems, scorched walls, and expended traps—to instill a sense of urgency.
- The Three-Way Fight: The elemental guardians hate the orcs just as much as they hate the PCs. Use this to your advantage. Have the players stumble into a room where Lzierabel is currently battling an Elder Air Elemental, forcing the party to choose who to attack first.
- The Innocent Host: Emphasize that Tiboquoboc is wearing Arezi’s body. Good-aligned parties must find a way to use Dispel Evil, Banishment, or Turn Undead to force the ghost out without killing the host.
Conclusion: A Masterpiece of High-Level Design
The Thunder Below is an incredible achievement in high-level adventure design. It provides a massive, fully-realized castle, a terrifyingly competent villainous team, and a dynamic timeline that prevents the players from simply resting after every encounter. If your campaign has reached the upper echelons of power, this is the perfect module to test whether your players truly deserve the title of “epic heroes.”
👉 [Race against the clock and claim your copy of The Thunder Below on DriveThruRPG]
Disclosure: If you pick up this adventure through my link, I’ll earn a few gold pieces from the Sarwin family vault at no extra cost to you.