Just in front of Vlaherna Monastery there is an island called Pontikonissi on which there is only one building: the church of Pantocrator. According to one interpretation of the Odyssey this island would be the ship of Ulysses that was turned into rock by Poseidon while, according to another legend would be the rock on which Ulysses' ship crashed during a storm.
The church of Pantocrator was built in the 13th century and to visit it you can take a boat from the small port opposite. The Byzantine chapel that is on the top of the island encloses the memorial tablets of Elizabeth Empress of Austria and Rodolfo archduke.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.