The Known World of Dungeons & Dragons began taking shape in the B/X edition, making D&D distinct from AD&D, which was set in the World of Greyhawk in the early 80s. My first contact with the Known World was from the map in the D&D Expert Rulebook (1981).

Grand Duchy of Karameikos

By 1990, Mystara (as the Known World would soon be “known” – ah, puns…) had been thoroughly mapped and populated far beyond Karameikos in the excellent Gazetteer series.

See also:
Gazetteer series at my reference site
The Eastern Countries Trail Map (1989): D&D Known World Setting

The Known World: It Isn’t Flat, But It Is Hollow!

TSR charted a new direction going inside the Known World. The project was helmed by the late, great Aaron Allston. One of my favorite RPG designers, Allston drew on drew on pulp fantasy Lost World literature – Think H. Rider Haggard, Edgar Rice Burroughs, et al – to populate the lands deep underneath Mystara’s crust.

“…this boxed set details not a subterranean realm filled with inhuman horrors or angst-filled dark elves but a lost world after the fashion of the pulp fantasies that inspired early D&D. This lost world is filled with anachronisms — ancient Greeks, Egyptians, Vikings, and Aztecs share the Hollow World with lizardmen, Hollywood-style pirates, high-tech elves, and Lilliputian animal-riders.”

Grognardia – Retrospective: Hollow World Campaign Set

“…this wonderful setting be attached & used for other old school & OSR D&D style settings. … Different caverns & tunnels of the Hollow World have planar gateways into other D&D settings even though many of these are monitored & very dangerous. There’s also the ‘spell of preservation’ issues along  lots of other weird bits & pieces.  Plus one has to deal with the Council of Intrusion ( the council is a party of immortals whose job is to eject any demons, devils, aliens, or cosmic entities from Mystara) if you were going to do a large scale otherworldly invasions you might be in trouble. But smaller parties, lone travelers, adventurers, etc. are not even going to be noticed.” 

Swords & Stitchery – Exploiting The Hollow World Setting & OSR Games

Hollow World Campaign Set

1990 … Aaron Allston … TSR 1054 … 3 books, 4 poster maps … ISBN 0880388625

Check Wayne’s Books Inventory

Check eBay

These box sets are now collector items, with collector prices. Gamers: If you just want to run a Hollow World game, DriveThruRPG is your go-to. You can buy in PDF ($10 – as of this writing) or Paperback reprint ($16).

One of the few times I’ve seen TSR printing anything on the box bottom side panel. Promoting some of the follow-on modules and accessories. This post is about the core set, so see my HW reference page for more info.

Dungeon Master’s Sourcebook

The 128-page DM’s Sourcebook (TSR 1054XXX1401), with that awesome Fred Fields art from the box lid.

I was alerted by “morphie” on the Piazza… Typo: TSR 1054XXX1901 is noted on the title page, but 1054XXX1401 on the back cover. The other two books have similar discrepancies.

Table of Contents & Credits

The DM’s book is all-business, with little interior art.

Player’s Guide

64-page Player’s Book (TSR 1054XXX1402)
Table of Contents

32-page Adventure Book (TSR 1054XXX1403)
Table of Contents
The Adventure Book has the requisite “get the party to Hollow World” adventure. There are actually a number of ways to get to this Lost World. See also: Known World to Hollow World: Atruaghin’s Mystical Conveyor in D&D GAZ14

The Maps

The first two maps are continental: 1054XXX0701 – Southern Iciria & 1054XXX0702 – Northern Iciria
Second pair of maps are thematic in nature, explaining the confusing relationship between Known World and Hollow World. 1054XXX0703 (presumed, no code printed) & 1054XXX0704.

Check Wayne’s Books Inventory

Buy at Amazon

Check eBay

Buy PDF and/or reprint at DriveThruRPG

Links to Amazon, DriveThru, eBay are affiliate links of course. I get a few coins and its costs you nothing. Thanks!

See also: Ready to deep dive into Hollow World? Check out the Hollow World subforum at The Piazza

Night’s Dark Terror (B10): TSR UK expands D&D’s Known World (1986)

D&D Wrath of the Immortals: The Geography of Mystara’s Cataclysm (1992)

B/X D&D Basic Rules book: 1st print vs subsequent prints

Which BECMI D&D Expert Rulebook do you have?