Dungeons & Dragons is known for the titular dungeon, but its origins are a little more prosaic than wargames alone. It turns out there was a formative experience in co-creator Gary Gygax's life that would inspire dungeon exploration.
A Link in the Chainmail
It's telling that Chainmail, Gygax's rules for miniatures combat, featured mines but not dungeons. Jon Peterson explains in Playing at the World:
While Chainmail obliquely mentioned the use of pen and paper to represent mines beneath castles (digging under walls being a recognized, if tedious, manner of circumventing defenses in the medieval period), Gygax never suggested that an underworld might be a suitable venue for gaming. The purpose of this paper record in Chainmail is to preserve the secrecy of mining operations: “While the defender will always know where these men are located,” that is, where the miners broke ground, “he will not know if they are actually at work on a mine,” nor more significantly where the tunnel extends. The referee maintains the paper, and draws the direction of mines and counter-mines in accordance with the instructions of the players.
In essence, Gygax established the "fog of war" mechanic in D&D as a means of keeping players in the dark -- an integral part of dungeon exploration being revelation of the unknown, room by room. The dungeon exploration we are familiar with today had its roots in co-creator Dave Arneson's Blackmoor. Shannon Appelcline explains in Designers & Dragons -- the 70s:
...the Black Moors were run as a campaign, with players eventually gaining experience from episode to episode. Throughout 1971 Arneson’s group fought fairly typical miniatures battles — facing off with the forces of the “Egg of Coot.” Then, in late 1971 or early 1972, the heroes moved to a new battlefield: the dungeons beneath and around Castle Blackmoor — a castle that originated in a plastic kit of a Sicilian castle that Arneson owned.
Peterson explains what happened next:
Arneson borrowed this pen and paper to keep his players in the proverbial dark while they explored his dungeon. He gave them information only about their immediate, claustrophobic surroundings, leaving it to their ingenuity to navigate their way to the ultimate depths, to say nothing of the way out. The result little resembled a traditional wargame: it was more a game of exploration, negotiated verbally with the referee, punctuated by bursts of combat.
Gygax's collaboration with Arneson would take dungeon exploration at a whole new sub-level.
"You Stand Before a Chain-Link Fence..."
Michael Witwer describes Gygax's experience in Empire of Imagination:
It was spring and the day was brisk. The boys stood in a driveway off Main Street that hadn’t seen use for many years. The rusty chain-link fence was in poor condition, having been compromised numerous times over the last many years. A crude sign on the fence advised KEEP OUT— NO TRESPASSING. This, paired with a more formal but tattered sign inside the fence’s perimeter reading OAK HILL SANATORIUM, served as a clear invitation for the boys to enter.
There's scant information about Oak Hill Sanitarium and for good reason, as Larry Hamilton observes:
Gary called it the Oak Hill Sanitarium. It was actually the Oak Wood Sanitorium on Catholic Hill, so Oak and Hill were put together, causing the difficulty. When Gary was young, the building still stood and the steam or laundry tunnels were still accessible. There were also holding cells, very much a dungeon setting.
The sanitarium is known by a few different titles, including Oakwood Sanitarium:
The sanitarium was opened in 1884. It was abandoned after World War II, and the story goes that locals were plagued by screaming coming from the empty building. As prime real estate, It was torn down years ago and built over but, according to rumor, that hasn't slowed down the former patients at all...
Lisa M. Schmelz picks up the thread in her article, "Mysteries of the Mind," where the sanitarium is referred to as Oakwood Springs:
Opened on May 13, 1885, Oakwood Springs was built at the then-astonishing cost of $80,000. Its treatments for diseases of the brain and nervous system were, at the time, the best the world could offer. In addition to promoting health via 63 acres of rolling hills and spectacular lake views, Oakwood’s attending physicians supervised a myriad of treatments. King would go on to acquire two other Lake Geneva properties and convert them into sanitariums. One was known as Lakeside, the other as Lakeside Cottage.
Witwer imagines how Gygax would have perceived the secret dungeon:
The natural beauty of Lake Geneva was no doubt considered therapeutic to those with mental illness, which may explain the prevalence of such institutions, usually given business names less ominous than asylum. The now abandoned and decaying buildings at Oak Hill were a perfect backdrop for an imagination as fertile as Gary’s, given fuel by circulating folk tales about escaped madmen and urban legends about prosthetic hooks found dangling from car doors by teenage lovers. Such tales would have hit very close to home for the population of Lake Geneva in the mid-twentieth century, to say nothing of a boy with Gary’s fascination with danger and intrigue... Legend held that Oak Hill, unlike many of its local counterparts, was for “very disturbed” patients who were subjected to an array of experimental and inhuman treatments. Adding to its intrigue, the doctor who owned and operated the facility allegedly went insane himself around 1910, which brought about the institution’s demise.
The Sanitarium eventually burned down in 1956.
Leaving the Dungeon
Gygax confirmed on ENWorld that a certain abandoned building inspired the exploration of dungeons in D&D:
Actually, the abandoned ruins of the five-story, red brick insane asylum (Oak Hill Sanitarium) that still stood here until c. 1958 were more influential in inspiring the D&D game than was the history you mentioned--the place had tunnels under it and "secret rooms" created by the boys who haunted the place.
As Witwer observed:
In the bowels of Oak Hill, the boys explored the “maze of tunnels,” crawl spaces, claustrophobic rooms, and secret passages that made up this veritable dungeon— a place, they thought, more appropriate for dragons, monsters, ghosts, and treasures than patients. Gary would later make it clear that there shouldn’t be “any doubts about where much of the inspiration for castle ruins and dungeon adventures came from . . .”
The dungeons we know today are a combination of Arneson's imaginative use of a toy castle and Gygax's childhood inspiration of a place -- whatever its name -- in which the mind was exercised in another fashion entirely.
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