Ah, the early ’90s when shoulder pads still lingered, mullets roamed freely, and TSR was still tossing glorious D&D settings at us like candy at a parade. Among the more ambitious entries of the time was The Hollow World Campaign Set (1990), a boxed set that cracked open the core of Mystara literally. Designed by Aaron Allston (yes, that Aaron Allston of Rules Cyclopedia fame), this setting turned the world inside out, dropped in a floating red sun, and asked, “What if the dinosaurs never died, the empires never fell, and gravity just politely reversed itself?”
It’s pulp fantasy wrapped in a lost world aesthetic, a love letter to Edgar Rice Burroughs and classic speculative fiction, all filtered through the crunchy, radiant lens of Basic/Expert D&D. It’s also a bit of a logistical headache if you’re the kind of DM who likes to ask questions like, “How do tectonic plates work here?” But for those who embrace weirdness and wonder, the Hollow World Campaign Set is a subterranean treasure trove.
Let’s strap into our magical elevator and descend through the crust of Mystara.
Table of Contents
Cracking the Shell: What Is the Hollow World?
For the uninitiated, Mystara is the default campaign setting of Basic D&D (as opposed to Advanced D&D’s Greyhawk or Forgotten Realms). It’s a land of heroic fantasy, flying ships, and Immortals instead of gods. But The Hollow World takes us beneath the outer world, into a giant inner sphere nestled inside the planet, where ancient civilizations have been preserved like particularly large, well-fed ants in amber.
How do they survive in this underground utopia? Easy by the light of the eternal red sun that floats in the exact center of the world like a Christmas ornament, shedding eternal twilight. No, there’s no day or night. Yes, that’s going to drive your clerics’ spell schedules a little bonkers.
But the core concept here is simple: The Hollow World is a magical museum, curated by the Immortals to protect cultures and species that would otherwise have been wiped out in the ever churning blender of surface world politics and wars. It’s part fantasy, part science fiction, and part philosophical thought experiment what happens when no civilization can truly fall?
The Boxed Set: What You Get
This 1990 boxed set came with:
- Two 64 page booklets: The Dungeon Master’s Sourcebook and the Player’s Book
- A gorgeous full colour map of the Hollow World
- A big ol’ hex map for tracking exploration the old school way
- A cutaway view of Mystara’s interior that belongs on your wall next to your vintage National Geographic posters
The Dungeon Master’s Sourcebook contains most of the juicy stuff geography, civilizations, rules for migration, and setting specific magic restrictions. The Player’s Book gives an in universe overview of the Hollow World, a primer for characters lucky or unlucky enough to find themselves stuck in this timeless land.
Pulp Fantasy Vibes: Influences and Atmosphere
The Hollow World doesn’t try to hide its inspirations. If your mind goes straight to At the Earth’s Core by Edgar Rice Burroughs or Journey to the Center of the Earth by Jules Verne, you’re not wrong. There are flying dinosaurs, ancient empires stuck in cultural amber, jungles the size of continents, and magical technology that doesn’t obey the rules you’re used to.
But where those older works often dipped into Victorian colonialism (with all its problematic baggage), the Hollow World takes a different tack. The various cultures here aren’t “primitive” in any moral sense they’re preserved, sure, but they’re often thriving in their own way. There’s an air of melancholy to it, too. These societies are museum pieces, and they can’t leave. Ever.
It’s like Night at the Museum, but with more lava men and less Ben Stiller.
Welcome to the Inner World: Geography and Physics
The Hollow World is a sphere within a sphere. It’s essentially the inside of a massive planetary chocolate egg. Its inner surface is habitable lush, vibrant, and perpetually under the glow of a motionless red sun that hangs at the world’s centre. This sun doesn’t rise or set, and there’s no moon. There’s also no weather in the traditional sense, no real seasons, and magic is a bit… different.
Travel between the outer world and the Hollow World is extremely limited. The most common method? Magical portals or freak accidents. This means adventurers rarely go there intentionally and once they do, getting out is a challenge.
Physics is also weird here. Gravity pulls “down” toward the crust, not toward the red sun in the center. So from a character’s point of view, you’re walking on the inside of a ball. You can look up and see the far-off landmasses on the opposite inner surface. It’s a wonderfully disorienting reminder that this setting is literally inverted fantasy.
Civilizations and Cultures: A Lost World Sampler Platter
The Hollow World is home to a number of cultures plucked from the brink of extinction and lovingly plopped here by the Immortals. But these aren’t just carbon copies of Earth civilizations they’re fantasy analogues infused with their own mythologies and quirks.
A few highlights include:
- The Azcans: A thinly veiled Aztec-inspired culture, complete with ritual blood sacrifice, pyramid temples, and obsidian weapons. Don’t expect them to hold hands and sing “Kumbaya” they’re in constant conflict with their neighbors.
- The Nithians: Ancient Egyptian inspired magic users who were erased from surface world history due to dangerous magical experimentation. In the Hollow World, they get to try again with some restrictions.
- The Milenians: Greco Roman imperialists with a love for grand architecture and epic oratory. They’re constantly trying to conquer their neighbors, because old habits die hard.
- The Neathar: A generic “ancient humans” culture tribal, widespread, and caught in a thousand internal conflicts. Think of them as your default barbarians with a Bronze Age aesthetic.
- The Beastmen: Failed magical creations and humanoid rejects who have formed a crude but stable society of their own. It’s messy, violent, and weirdly endearing.
Each of these civilizations is stuck in its own cultural loop. This isn’t a flaw it’s intentional. The Immortals use magical “Spell of Preservation” fields to prevent social evolution. Innovation is discouraged. Empires don’t rise and fall they just are. Imagine playing a campaign where the real villain is progress, and the gods themselves are museum curators with a strong opinion about iPhones.
Magic with a Twist
Magic works a bit differently here, and that’s part of the fun. First off, the aforementioned Spell of Preservation affects spellcasting. Spells that tinker too much with knowledge, transportation, or planar communication tend to fail or just explode.
Clerics are hit especially hard. Many surface deities have no power here, so unless your cleric worships one of the Immortals recognized in the Hollow World, you might want to invest in a backup career as a herbalist. Even when divine magic does function, the cultural restrictions on thought and innovation make certain forms of magic taboo.
Want to introduce gunpowder? Too bad. The Spell of Preservation ensures that even if you invent it, nobody else will believe you. Your musket is now a decorative stick.
Running a Hollow World Campaign: Tips and Shenanigans
The Hollow World isn’t your average campaign setting. It’s isolated, strange, and designed to be a closed loop ecosystem of adventure. Here are a few ways you can make it shine at your table:
1. Shipwrecked in the Hollow Earth
One classic way to start a Hollow World campaign is to have a group of surface world adventurers accidentally stumble in via magical storm, ancient teleportation circle, or “Oh no! We fell through a sinkhole the size of Rhode Island!”
This outsider status gives players a chance to marvel at (and be confused by) the culture locking magic, the red sun, and the inverted horizon.
2. Native Heroes Breaking the Cycle
Flip the script by having players start as Hollow World natives who begin to question their own society. What happens when a Milenian hero starts dreaming of democracy? What if an Azcan priest stumbles on a forbidden library? Run a campaign about cultural resistance, revolution, or attempts at contact with the outside world.
Good luck, though the Immortals will be cranky about it.
3. Jurassic Dungeon Crawl
There are plenty of monstrous denizens here too carnivorous dinosaurs, ancient horrors, magical experiments gone wrong, and, of course, other adventurers who never made it out. The jungle is thick, the temples are ancient, and the traps are plentiful.
It’s a great excuse to run a pulp style mega dungeon or hexcrawl campaign.
Legacy and Influence
The Hollow World Campaign Set didn’t get quite the love showered on the Forgotten Realms or Dragonlance settings, but it developed a dedicated cult following especially among those who love exploration, ancient cultures, and settings that twist the usual high fantasy tropes. Its best spiritual successor might be Dark Sun (with its own isolated ecosystem and oppressive divine control), but Hollow World has a charm all its own.
Aaron Allston deserves major credit for making this setting not just imaginative but also playable. It easily could have turned into a vague conceptual mess, but instead it’s surprisingly usable if you’re willing to embrace its unique rules.
The set also ties neatly into other Mystara products, especially the Wrath of the Immortals boxed set (which explains more about those meddling Immortals and their celestial management style). Later editions of D&D never really followed up on Hollow World, making it something of a lost artifact itself.
Which is, honestly, kind of fitting.
Final Thoughts: A World Preserved, and Worth Preserving
Dungeons & Dragons: The Hollow World Campaign Set is one of those beautifully weird TSR products that reminds us how wildly creative the early ’90s could be. It’s not just another fantasy world it’s a radical departure from the norm, a place where history gets frozen in amber, where the gods meddle with anthropology, and where dinosaurs might trample your magic user before lunch.
If you love the idea of pulp fantasy, of sandbox campaigns with ancient secrets, of breaking your players’ brains with an inside out map and eternal twilight then dust off your boxed set, roll up some hexes, and take the plunge into the Hollow World.
Just don’t expect to leave. The Immortals are watching.
