The Great Wall of China is the greatest symbol of ancient Chinese engineering and one of the world's most famous structures.
Built to protect the northern edge of the Chinese empire against invasions from Mongolian nomads. The Wall was never that effective against Mongol invasion, but eventually the threat abated anyway as the Mongol nomads were converted and assimilated.
A wander on the Great Wall will take you back to the Ming empire as well as offering you sweeping views of the surrounding countryside.