Player characters begin by arriving at the keep which they can adopt as a base before investigating the series of caverns in the nearby hills that are teeming with monsters.
Plot twists include a treacherous priest within the keep, hungry lizardmen in a nearby swamp, and a mad hermit in the wilderness.
It consists of a 32-page booklet with an outer folder; the module was written by Gary Gygax, with cover art by Jim Roslof and interior illustrations by Erol Otus.
[5] Jon Peterson, for Polygon, highlighted that Keep on the Borderlands was created after "sales of the Basic Set rose dramatically" following the September 1979 disappearance of James Dallas Egbert III.
[6] Anders Swenson reviewed The Keep on the Borderlands for Different Worlds magazine and stated that "It is well balanced, and suitable for the levels of characters for which it was written.
"[8] Lawrence Schick, in his 1991 book Heroic Worlds, described the adventure as "A good start for new players" and speculated that at the time, "There probably have been more copies of B2 printed than of any other role-playing scenario.
[...] Because Keep on the Borderlands would ship with the Moldvay Basic Set, at the height of the D&D boom in 1981, it became one of the most widely known modules in D&D history, selling 750,000 copies a year.
[6] The French RPG magazine La Gazette du Donjon gave this adventure a rating of 3 out of 5, saying, "The fortified castle on the borders of the country is a very open introductory module in the sense that it gives free rein to the imagination of the players (and the dungeon master).
"[13] In his 2023 book Monsters, Aliens, and Holes in the Ground, RPG historian Stu Horvath noted that this adventure "seems to be the culmination of design experiments that were taking place in the industry at large."
The original B2 publication was generic in terms of setting, while the 1999 Return module placed the Keep in Yeomanry, making it a canonical location in the World of Greyhawk.
In September 2010, the module was re-released for D&D 4th Edition by Wizards of the Coast for use in the weekly D&D Encounters sessions as Keep on the Borderlands: A Season of Serpents.
Like the original, this revised module was designed for use with the contemporaneously released Dungeons & Dragons Fantasy Roleplaying Game boxed set for D&D Essentials, which is oriented towards the beginning player.
Nonetheless, many GMs found the adventure too long—mainly because it made it hard to bring in new players late in the season, something that matters more in an organized play environment".
[18][19][20] In 2016, the Brazilian publisher Redbox Editora released a remake of The Keep on the Borderlands called O Forte das Terras Marginais for their own retro-clone system Old Dragon.
[23] In January 2018 Goodman Games announced that the hardback book would be 380 pages in length and contain digital scans of the originals, 5th Edition conversions, additional new content, and "testimonials".