As your party emerges from the tangled brush, briers, and vines that fence the Old Castle Track, you observe the sprawling ruins of an enormous castle complex built upon a sloping bluff of rock. Crumbling, battlemented walls join towers square, round, and pentagonal. Gatehouses, courtyards, and craft shops lie in varying states of disrepair. High above the ruins, at the culmination of the bluff, rise two impressive towers: one round, the other hexagonal. The great east towers flank an enormous fortress of stone from which carved spires rise, piercing the very sky. This edifice can be none other than Castle Zagyg, the dwelling of the Mad Archmage.
Your quarry looms ahead! Explore the ruins at the foot of Castle Zagyg, plunge within the murky caves that dot the rocky bluff, or make for the castle fortress, seeking ingress to Mad Archmage's many and sundry dungeons below -- your choices are myriad. Adventure and derring-do beckons, seekers, though discerning individuals will no doubt note that a horrible death is as probable as attaining both fame and vast treasure. Are you and your fellow explorers brave enough to undertake the challenge, the mystery, the weird whimsy and lurking horrors that are Castle Zagyg?
Gygax with Kuntz later retconned the basement of Castle Greyhawk to have 50 levels instead of just 13, and removed Zagyg as the architect. Zagyg was written back into the story as a demigod whose domains were puzzles, secrets, and practical jokes.