Vlad the Impaler's Prison is a secret location and side memory included within Assassin's Creed: Revelations. It was available to those who purchased the Collector's Edition, the Animus Edition, the Signature Edition or the Ultimate Bundle Edition of the game. It is also made available to those who purchased The Lost Archive downloadable content.
After the Ottoman general and covert Assassin Ishak Pasha defeated Vlad the Impaler in conflict in 1476, Sultan Mehmed II held his head and his legendary sword in a prison outside the borders of Constantinople, in the fear that doing so would prevent Vlad from coming back from the dead, based upon rumors of his infamy.
In 1511, the Assassin Ezio Auditore da Firenze traveled to Constantinople, and after learning about the prison from a book in Sofia Sartor's book shop, took to the sewers from an entrance in the side of the city's bordering walls to a secret prison outside of Constantinople. Once there, he traversed many free running obstacles in order to claim Vlad the Impaler's blade from his coffin, a weapon once rumored to be able to defeat any foe.