The Oracle of Trophonius was one of the four Oracles associated with Apollo. It is also probably the most dangerous. The petitioner would enter and drink from both the fountain of memory and the fountain of forgetfulness in order to prepare the mind. Assuming he or she did not die, they would go to the Cave of Trophonius where they would experience untold horrors from which came "nightmarish verse." Assembled properly, the nightmarish verse. Once the petitioner came out of the cave, assuming he or she was not driven insane (or died), he or she would sit on the Throne of Memory and the verse would come out. The priest wrote down what the petitioner said and that would be a prophecy. Without the Throne of Memory, the petitioner would forever be trapped with horrors of the cave.
The Oracle of Trophonius is currently located in Bluespring Caverns, Bedford Indiana. While there the spirit of Trophonius asks for a favor. He asks Apollo to destroy the cave thus making the oracle in-excessable to anyone. Trophonius mentions that the location is too exposed and that Commodus would keep sending men down. Grudgingly Apollo agrees which is why when he leaves the cave and encounters three Blemmyae he makes no attempt to stop them from blowing up the cave.