Horse Keeper's Key

The Horse Keeper's Key is a special golden key-like item that Theseus had. Theseus is supposedly the "keeper" of the Steeds of Time when Kratos meets him. Kratos then defeats and kills Theseus, taking the key for himself. With it, Kratos is able to unlock the doorways that allow him to enter and traverse the alters of the Steeds of Time. He then uses the key to free all four steeds from their bridles.