Expedition to the Ruins of Greyhawk is a Dungeons & Dragons super-adventure, designed for characters of level 8-13, that revisits Castle Greyhawk and the classic dungeon beneath. Significant background information is provided on the City of Greyhawk as a base of operations for the players, and as a mini-campaign setting of its own. This adventure is usable as a mini-campaign, a story arc in a Dungeon Master's regular campaign, or as a series of small side adventures with a big payoff. Like other adventures in the "Expedition" series, this product takes a classic Dungeons & Dragons location, updates it for D&D v.3.5, and incorporates many new twists and surprises. This adventure also includes useful source material for players and a combat encounter format designed to make the DM's job easier.