The Guild Cave is all that remains of the Heroes Guild.
The people of Albion started a revolution, burning the Heroes Guild down and started killing the Heroes. During the 500 years between Fable/Fable: The Lost Chapters and Fable 2, it is buried and the ruins of the Heroes Guild become located beneath Bower Lake.
During the course of Fable 2, Sparrow goes underneath Bower Lake to explore the caves. The series of tunnels eventually leads to the Chamber of Fate, which had not been damaged too much. During later stages of the game, The Chamber is used as a hideout for the Heroes to plan the next attack against Lucien Fairfax.