Hohenbaden Castle, built in 1102, and known locally as the Altes Schloss (Old Castle) was home from the 11th-15th century to the margraves of Baden. During its heyday in the 15th century, the castle had 100 rooms. In 1479 margraves moved their seat to Baden and the old castle started to decay. In 1599 it was destroyed by fire.
From the tower you have a good view over Baden-Baden and distant view of the Rhine valley. The courtyard of the ruins is also worth of seeing.
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.