"To the east of the busy walled city of Greyhawk the land is forsaken, overgrown with thorns and thistles. Oozing marsh creeps slowly down. The copses are huddles of weird, bloated trees. The wiry grass seems to grasp at the feet of any who dare to tread upon it. In the center of this unwholesome place, on a rock-boned prominence, hulks the ruin of the grim Greyhawk Castle..."
"The fallen west gate of Greyhawk Castle was at hand, and through this mouldering portal the party passed. In a few moments they had entered the great central keep, heaved open an inner door, and carefully proceeded down a set of winding stone steps---steps worn with age and slippery with dampness. They had entered the dungeons."
Castle Courtyard with Keep
"... Old Greyhawk Castle was 13 levels deep.
The first level was a simple maze of rooms and corridors..."
|Castle Greyhawk Level 1|
"The second level had two unusual items, a nixie pool and a fountain of [endless] snakes.
The third featured a torture chamber and many small cells and prison rooms..."
|Castle Greyhawk Level 3|
"The fourth was a level of crypts and undead.
The fifth was centered around a strange font of black fire and gargoyles.
The sixth was a repeating maze with dozens of wild hogs (3 dice) in inconvenient spots, naturally backed up by appropriate numbers of wereboars.
The seventh was centered around a circular labyrinth and a street of masses of ogres.
The eighth through tenth levels were caves and caverns featuring trolls, giant insects, and a transporter nexus with an evil wizard (with a number of tough associates) guarding it.
The eleventh level was the home of the most powerful wizard in the castle. He had balrogs as servants. The remainder of the level was populated by Martian white apes, except the sub-passage system underneath the corridors which was full of poisonous critters with no treasure.
Level twelve was filled with dragons.
The bottom level, number thirteen, contained an inescapable slide which took the players “clear through to China”, from whence they had to return via “Outdoor Adventure”.
It was quite possible to journey downward to the bottom level by an insidious series of slanting passages which began on the second level, but the likelihood of following such a route unknowingly didn’t become too great until the seventh or eighth level
Side levels included a barracks with orcs, hobgoblins, and gnolls continually warring with each other, a museum, a huge arena, an underground lake, a giant’s home, and a garden of fungi."
 Art (uncredited) from Outdoor Geomorphs Set One: Walled City by Gary Gygax (TSR, 1977). The sample encounters from this set reference City of Greyhawk locations, so the art is possibly a picture of the city.
 Excerpts from The Expedition into the Black Reservoir by Gary Gygax (El Conquistador, 1975).
 "Bodenburg Castle was used as the original model for the ruined upper works of Greyhawk Castle. Gygax had one in his basement at 330 Center Street" - caption for historical display by Paul Stormberg at Gary Con VI. Photo is by Allan Grohe (grodog).
 Siege at Bodenburg Map Inset. Source: The Army Men Homepage.
 Excerpt from "How to Set Up Your Dungeons & Dragons Campaign" by Gary Gygax (Europa #6-8, April 1975) & "'Greyhawk' had a fountain on its second level which issued endless numbers of snakes" (Greyhawk, 1975).
 Two Levels of the Real Castle Greyhawk by Random Wizard (2013). See also Gygax Castle Greyhawk Map thread at the Knights & Knaves Alehouse. These were maps that Gary was using to run the Castle at conventions in the last decade of his. Please note that these maps, while appearing old, may not be the original maps for these levels; notably, the first dungeon level of the published Castle Zagyg uses a different map.