Olbrück Castle is a hilltop fortress with a diamond-shaped floor plan. The central feature of the castle is the 34m high main tower, which dates back to the mid-14th century and is the oldest preserved part of the structure. Today, these rooms serve as museum spaces where visitors can learn about the construction history and function of castles. From the tower's roof, visitors have a panoramic view of the Rhine River to the east, the Ahr Mountains to the north, and the volcanic landscape to the south. On clear days, the Cologne Cathedral is even visible.
The castle was probably built originally in the 12th century. After several owners and reconstructions in the Late Middle Ages, During the Thirty Years' War, the castle was captured and devastated by Swedish troops in 1632. It was recaptured by Spanish and Electorate of Cologne troops under Graf Ernst von Isenburg-Grenzau in January 1633. Partially collapsed in 1660, the castle was subsequently restored under the supervision of Capuchin friar Bonitius from Linz.
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.