It is a citadel that contains the remains of several ancient buildings, such as the Parthenon and the Erechtheion, that symbolize the classical Greek civilization.
It is a complex of temples and palaces that was the capital of the Khmer Empire from the 9th to the 15th century and features the iconic Angkor Wat.
It is a 15th-century Inca citadel perched on a mountain ridge in the Andes and a masterpiece of engineering and architecture.
It is a rock-cut city that was the capital of the Nabatean kingdom and a trade hub in ancient times and is famous for its elaborate facades and tombs.
It is a series of fortifications that stretches over 21,000 kilometers and was built over centuries to protect China from invaders.