A Megadungeon Idea for Barbarian Conqueror King

This is a very rough idea of a megadungeon (or large dungeon smaller than a megadungeon) for my Barbarian Conqueror King setting for ACKS.

The idea is this: two decades ago, Harat’s corrupt (and Chaotic) sorcerer-king was overthrown by a slave revolt, let by Hardun the Lizardman Gladiator. The sorcerer-king himself fell to Hardun’s sword, and his mighty palace, overlooking the city-state of Harat, was smitten. But as the old palace is a reminder of the old regime, Hardun sees it as unfitting to sit himself on the sorcerer-king’s dread throne or even on its ruins. Now King Hardun (Lawful in alignment) rules Harat from a palace he has built in the (Hanging?) Gardens of Harat, a place of vegetation, and, more importantly, water (including heated water - King Hardun spends hours every day in his hot bath, especially during winter). The Gardens now also include public baths, built by the new King for his citizens to use free of charge.

So, in a nutshell, the old palace’s dungeons would serve as a megadungeon. What I’m trying to think about is how did this dungeon survive inside a city-state now ruled by people who oppose its creator? One idea I was thinking about was that Hardun has ordered a small Pyramid built on top of the old palace’s ruins, as a temple for Ixchala - the Lawful goddess of the Lizardmen. The Priestesses and their sanctified terraced pyramid guard against the dungeon’s inhabitants - various creatures of chaos and undeath, but so far Hardun and his Army of the Free have been unable to fully clear out this dungeon, especially since it extends under the city and connects to its sewers.

Or would a more remote palace of the sorcerer-king (maybe a Summer Palace outside the city) will be better for this purpose?

I definitely think a megadungeon in/under a city is a great idea.

The main megadungeon for my Crimson Sun campaign is located in and under the City of Tyr: the Ziggurat of King Kalak has eight tiers, with a base 800’ by 550’, each over 25’ high. Only a fool would attempt to enter it through the shrine on the top, where Kalak’s templars perform their rituals and sacrifices; but there are persistent rumors of secret entrances on the sides, as well as tales of tunnels connecting it to the labyrinths of Under-Tyr.

The insides of the ziggurat are full of traps, laboratories, libraries, embalming rooms, summoning chambers, ritual rooms, cells for monsters, magical gardens, and stranger things.

“Under-Tyr” covers everything underneath the city: the first several levels are ancient city blocks, built over and sunken throughout the centuries the “modern” city has existed; these are mixed with sewers. These upper levels are home to thieves, undesirables, escaped slaves, secret societies and cults, as well as grotesque freaks and ragamuffins (TBD). Some sections are ancient catacombs.

Deeper down, one begins to encounter the constructions of the Ancients: first the ruins of ancient city blocks, and then vast sewers and cleansing plants, as well as huge pipes, storage tanks, and water pipes that still fill the wells and irrigate the fields around the city (though every year they work worse and worse). The outer reaches of these tunnels connect to the vast caverns and windings crawls of the Underworld, through which inhuman monsters crawl into Under-Tyr, and even up into the alleys of the city…

It’s pretty much the Undermountain meets Barsoom’s underground ruins meets Fallout 3’s urban ruins.

What if your sorcerer-king was a load-bearing boss, and various sorcerous contingencies laid by generations of Chaotic lords caused the very structure of the building to alter in some way. The main doors sealed shut or disappeared, the hallways filled with opaque smoke, the forces of Law were sickened if too many entered, etc.

So, King Chaos was laid low by Lawful Guy. The very earth rose up and swallowed the main entryways, while the many windows and balconies collapsed or filled with iron-hard thorned plants. The lowest floors flooded with black mist which sickened the conquerors and raised the dead. King Hardun barely escaped through a secret tunnel, which he promptly built a Lawful temple on top of.

There are a few other secret entrances to this place, and it mostly sits quietly, brooding, a tomb to Chaos more than a monument to Law. Adventurers enter through the temple of Ixchala, or through the secret ways that the servants of Chaos are said to yet use on their errands.

I love this! This will mean there will be two temple for Ixchala in Harat - a small one, hastily built on top of the secret entrance to the sorcerer-king’s palace, serving as a guard over it; and a new one, still under construction, serving the faithful lizardman (nad human convert) congregation in Harat.

This will be called The Dark Underbelly of Harat and will involve the city state’s sewers, the old catacombs, and Chaotic warrens under the old, collapsed castle. Oh, and King Hardun knows about some the minibosses who dwell there and has a bounty on their heads…