The iconic, unnamed keep in module B2 "The Keep on the Borderlands" has been recreated in both Minecraft and Sketchup. A 3D printable version is available at MyMiniFactory. Some photographs of a scale model under construction were also shared, here.
Map of the Keep, from module B2 "The Keep on the Borderlands" (1980). Scale: one square equals 10 feet
The Keep is overseen by the Castellan, (described as a "governor or warden of a castle or fort" in the module's glossary). The AD&D 1e DMs Guide provides additional information concerning the role of a steward/castellan, in the "Hirelings" section, on page 34.
...the Keep contained multiple clerics but no chapel for their work. After considering the matter, especially the hectic schedule being kept by the Boss during this turbulent era, I took it upon myself to write up a suggested Chapel
EN World, March 30, 2005
Al did a phenomenal job, and went on to develop floor plans for the Common Stables and the Warehouse, as well. As a grand finale, he digitized and colorized a three-level map of the Fortress (based on designs contributed by Drew Williams).
(Alternately, check out Floor Plans for "Keep on the Borderlands")
The Keep was revisited in AD&D 2e's "Return to the Keep on the Borderlands" (1999) by John Rateliff, in which it was named "Kendall Keep" and given a more detailed history. An updated map of the Keep with some new features was included.
Also worth checking out, Snorri's blog "A Wizard in a Bottle" posted some interesting speculation about the Archaeology of the Keep, back in 2010.
Alternate versions of the Keep on the Borderlands have appeared in various publications, starting with Kenzer and Company's "Little Keep on the Borderlands" (2002):
3D representation of "Frandor's Keep", from Knights of the Dinner Table #100 (February, 2005). Reproduced as part II of the "Little Keep Web Extra", downloadable here.
Frandor's Keep was revisited in "Frandor’s Keep: An immersive setting for adventure" (2009) for the HackMaster RPG.
The next major revision of the Keep on the Borderlands was introduced in D&D 4e's "The Keep on the Chaos Scar" adventure, by Mike Mearls:
Illustration of "Restwell Keep", from "The Keep on the Chaos Scar" in Dungeon #176 (March, 2010)
Restwell Keep subsequently featured in D&D 4e's "Keep on the Borderlands: A Season of Serpents" (2010) by Chris Sims.
Finally, Dyson Logos posted his own version of the Keep, complete with some interesting tweaks, back in 2014.
Two years before "The Keep on the Chaos Scar" was published, Wizards of the Coast released its first introductory adventure for D&D 4e "The Keep on the Shadowfell" (2008), involving a different, ruined keep, more of a dungeon location.
"The Shadowed Keep on the Borderlands" (Raging Swan Press, 2012), by Creighton Broadhurst, designed for the Pathfinder RPG, draws greater inspiration from the Moathouse in module T1 "The Village of Hommlet", and is likewise a dungeon location.
In the section on "Designing Floor Plans" in module B2, Gygax suggests "you might wish to include a secret entrance to a long-forgotten dungeon (which, of course, you must design and stock with monsters and treasure)".
Kenzer and Company released beautifully rendered maps detailing a four level dungeon as a supplement to their "Little Keep on the Borderlands", downloadable as part of a free web extra in Beneath the Little Keep (2005).
(Although the layout of "Frandor's Keep" differs in some ways from that of the original Keep, access to the dungeon is through the Fortress in the Inner Bailey, and can be used with the original module).
Fifth Edition Fantasy #14 "Beneath the Keep" by Chris Doyle, released as part of Free RPG Day in 2018.
Goodman Games subsequently released the brief adventure "Beneath the Keep" (2018) as a tie-in to OAR#1 "Into The Borderlands", involving a smaller dungeon accessed through one of the buildings in the Outer Bailey.
Siege on the Borderlands:
With such a detailed map, several groups have played out sieges using the Keep on the Borderlands (we did). Rules for conducting sieges may be found in Chainmail (pg 22-24), or the more extensive D&D Master's Set siege machine rules (pg. 23-32).
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