The Deepest, Weirdest, Hugest Megadungeons Ever Created

The megadungeon is a cornerstone of fantasy role-playing games. Level upon level of twisting corridors and nefarious rooms filled with monsters, traps, puzzles, and magical treasures. These are the best megadungeons of all time, from D&D and beyond.


This was my first exposure to the megadungeon concept, and it was love at first sight. Undermountain (pictured above) is a massive complex built beneath the city of Waterdeep in D&D's Forgotten Realms campaign setting. At first a dwarven mithril mine, later invaded by drow and duergar, and eventually expanded and filled with monsters and traps by the Mad Wizard Halaster, it's something of a proving ground for adventurers who seek to learn Halaster's secrets. Undermountain's many levels contain temples, gates to other planes, an entire pirate city, and it connects to the Underdark, which is basically an entire subterranean world.

Space Hulk

The idea of a megadungeon works well beyond sword and sorcery. Set in the Warhammer 40K universe, Space Hulk has appeared in many incarnations, including a board game, card game, and several video games. In each iteration, your squad of space marines has to explore a derelict spaceship filled with genetic mutants, bizarre aliens, and myriad environmental hazards. While not every game of Space Hulk takes place on a massive map, the ships you explore are conceptually enormous. Players have built huge Space Hulk sets and combined multiple games into enormous mazes at game conventions.


Blackreach is a signature location in Elder Scrolls: Skyrim. It's semi-abandoned underground city filled with eerily beautiful glowing mushrooms, strange ruins, rare plants and other oddities. The first time you delve into Blackreach, you can't help but be a bit awestruck. The silence down there is intense, creating a tension and wonder I've rarely experienced in video games. Blackreach itself is massive, but to get to it you actually have to work your way down through another dungeon, a Dwemer ruin. And Blackreach is actually connected to three of these dungeons, so there's no doubt it's worthy of the "mega" appellation.

Castle Greyhawk

This is a somewhat mysterious megadungeon because few people have ever truly seen all of it. Various publishers have put out versions of it over the years, but most of the castle and the dungeon complex beneath it were designed by D&D creator Gary Gygax for his personal campaign. Some of the published versions have included input from Gygax, some were adapted from his notes, some had nothing to do with Gygax at all. The glimpses we have of his original ideas, published in some very early gaming magazines in the 1970s, reveal that Gygax was always a mad genius.

"The eleventh level was the home of the most powerful wizard in the castle. He had Balrogs as servants. The remainder of the level was populated by Martian White Apes, except the sub-passage system underneath the corridors which was full of poisonous creatures with no treasure. Level twelve was filled with Dragons."

The Death Star

Even if you account for the large core being taken up by the reactor, the Death Star is still a space station the size of a moon filled with winding corridors, prison levels, strange caverns, plenty of storm trooper goons to battle, and a couple of big bads . There must be thousands of miles of corridors to explore. It would be fun to re-skin the Death Star for a fantasy RPG. "It's not impossible. I used to bullseye wererats with magic missile back home."


The megadungeons of Minecraft aren't one specific dungeon, but the randomly generated caverns you find in Minecraft provide some of the most viscerally exciting explorations in all of gaming. It's hard to explain if you haven't experienced it, but when you're digging deep underground and break through to the inky depths of some massive cavern complex and hear the terrifying sounds of monsters lurking somewhere in the darkness, a serious chill goes up your spine. Minecraft's dungeons can be claustrophobic mazes that suddenly open into gorgeous vistas, like an underground canyon with a lava river pouring down a huge cliff. You might find abandoned mines, rare treasure, and even portals to other realms.


One of the seasons of D&D Encounters (the weekly in-store organised play program for D&D) was called Dead in Thay, and features the Doomvault, a tribute to classic megadungeons from D&D's past. You can also purchase a pdf of the adventure and run it with your own gaming group. If you're not sure if a brand new megadungeon can stand up to the classics, consider these two factors: it has an area called The Forest of Slaughter, and it was designed by Scott Fitzgerald Grey. Forest of Slaughter, people. Forest. Of. Slaughter.

Ministry of Magic Headquarters

In the Potterverse, the Ministry of Magic's London HQ is a ten-story building located entirely underground. We only get to see a few parts of it in the books and films, but it's enough to get a sense for how massive the place is, and the bizarre things you might find there. Lots of it is just offices and corridors, but there are archives filled with magical prophecies, and it's easy to imagine you'd find spellbooks, strange ingredients, and even magical creatures being studied in level nine's black-tiled Department of Mysteries.

Temple of Elemental Evil

This temple isn't filled with your basic generic brand processed evil. You won't find evil mixed with non-evil additives. This temple is filled with raw evil. Pure evil. Unadulterated evil. Elemental evil. First released in 1985 for the first edition of Advanced Dungeons & Dragons, Temple of Elemental Evil is a gaming group crucible. It's so deadly you might get killed by giant frogs before you even enter the damn dungeon. If you avoid the numerous insta-death traps and other Gygaxian treachery, you might actually wind up battling a demon.


Think about it.


    Lol ikea. But man, first thing I thought of reading that headline was Blackreach. Just stumbled upon that one day after like 70 hours worth of play, and man. Awestruck is the right word. After getting so used to the way all the other dungeons in that game worked, it was a sight.

      Agreed! The thing about Blackreach is its darn dark. And eerie.. And darn big and confusing and the mini-map only shows one small portion at a time. Did I mention big and dark? Gotta love the Skyrim.

      Blackreach was easily the best part of Skyrim. Went to Markarth afterwards and haven't returned to the game since.

    You realize megadungeon means million dungeons...

    Minecraft? Try Terraria. You are happily mining ores deep within the ground, following a particularly promising vein, and suddenly your pickaxe breaks into empty space, the light of your torch faintly hinting at a massive open space on the other side. And then the sound of scuttling or flapping of wings...

      That so feeds in to my D&D campaign Idea. Magic and Dragons have been extinct a few thousand years and the world is a cruel place ruled by the BBEG. The PCs village is raided and they are marched overland to the deepest Dungeon where the PCs are put to work mining for artefacts of the past. Now they break through into a cavern with a million dragon eggs. The temperature change triggers a mass hatching as tiny dragons pursue the populace through the caves and caverns and dungeons looking to escape to the surface.

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