Greyhawk Castles

The historical Greyhawk Castle underwent major iterations, each with a different level structure, from the original version of Gygax to a revised version run in combination with Rob Kuntz, to an abridged version for convention play, to the published fragment. 

• 1972 -  Old Greyhawk Castle ("1st Castle") 13 levels, about 7 side and extra-planar levels
• 1974 - Expanded Greyhawk Castle ("2nd Castle") - 44 core levels, about 60 total
• 2004 - Abridged Greyhawk Castle, based on Old Greyhawk Castle, used at conventions and in a home campaign, 6 or 7 levels
• 2007 - Castle Zagyg - planned 25 levels, 16 main; Only ruins and first level were published

The Old Castle is the one that birthed D&D. The players reached lord level (level nine), erected three towers on top of the ruins and remodeled the first level. 

The Expanded Castle replaced the Old Castle in the middle of 1974, when Rob Kuntz was enlisted as Co-DM as there was too much player demand for Gary to handle. [15] This means any stories after mid-1974 relate to the Expanded castle. It merged Gary's and Rob's dungeon, and some of these levels are conserved as scans in the El Raja Key Archive, some even with key. They sport the same labyrinths, thin walls and minimal, random-feeling monster keys. Some levels of  his were later published as Maure Castle in the module Mordenkainen's Fantastic Adventure.

To be frank, the castle changed over the years, so "original" is moot. As levels were added by me, new and different things were introduced. When after a couple of year's of time Rob became my co-DM there was a massive alteration in the upper works of the castle, a whole, massive new 1st level was created, and then the level plan for the expanded lower levels of the dungeon was created anew, with the original levels of my making incorperated with those of Rob's dungeons, plus a number of new ones we created to fill the whole scheme.

We had about 40 or so levels, plus side excursion levels reached by transporter locales. Some of the levels were done on 22" x 17" graph paper of [four] or five lines per inch, some on standard size sheets with varying lines per inch--4, 5, 6, or even eight. One level was done on paper with a hex grid. [35]

The Convention Play / Abridged Castle reused the Old Castle level maps, and is thus a major source of knowledge about how the original dungeon looked, at least the first few levels. The first and third level were photographed, for the first level even the map key is decipherable on the photo. Furthermore, there are play reports, from convention play, from a session with the moderators at EnWorld, and from the home campaign.

The last version, Castle Zagyg, was Gary's effort to publish the dungeon, so others could run it. Gary newly invented most of the upper works and outer caves. The Storerooms map was based on the first level of the Expanded Castle, with four major areas controlling access to the four stacks of deeper levels.

There are also attempts at reconstruction from others:

WG7 Castle Greyhawk - is a shitty travesty that TSR published to ridicule Gary after he had been ousted. Many including me think this is the worst adventure ever to see print, because the gap between your excitement of what you will get, and what you actually got is so abysmal. I certainly was as dejected as Bryce Lynch when I bought this before I realized what it was. 

WGR1 Greyhawk Ruins - this is the "official" version from TSR. Supposedly OK because it reflects some ideas from the original, like the three keeps, and is a solid effort as a standalone module, it does not use the original maps or levels. Expedition to Castle Greyhawk is the 3e conversion

Castle of the Mad Archmage, by Joseph Bloch is a fan-reimagination, and has been called the spiritual heir of the original. However, the first level already does not match either of the two known first level maps from the Old Castle or the Expanded Castle, so: nah. Not that it matters. Allan Grohes Version, likewise is a re-imagination, but not published as a module.

Castle Greyfalkun, was announced by Rob Kuntz based on his levels and recollections. While he does not have the rights to some of the core material, and lost his Expanded Castle maps, Gary recounts stories about Robs acute memory, and Rob co-ran the Extended castle, so if this ever should get published it could be interesting. No news however since 2019, so don't hold your breath.

The original maps and keys still exist as part of the Gygax Estate. His estate is not showing any progress to release the "nearly 100 pages of Gary's hand drawn maps, keys, notes, and drawings", so we may never know. Even if they get eventually published, if we extrapolate from the level we know, level one, they might meet a similar reception as Castle Blackmoor. There is nothing there that would recreate an extraordinary play experience. 

Along with the castle, there were also at several iterations of the game world, fist the simple wilderness version, then the published World of Greyhawk. Here is a nice overall writeup. 

Many of the clues we have come from play reports and due to the fluid nature of the dungeon, many of these reports contradict each other, and Greyhawk Castle will may forever remain shrouded in mystery.  I imagine Gary would would have enjoyed this. After all, this was the man who proclaimed in his DMG: Keep the mystery high at all times: wonder, excitement (and PC/Player fear) will soon follow. 

[References: see Greyhawk References]