Beijing: The Great Wall

The Great Wall was built between the 5th Century BC and 16th Century AD for protection and as a military communications route. From the 17th Century on it was left to crumble away, aided by peasants who used portions for their own buildings.

The portion of the Great Wall which is most popular with tourists is at Badaling near Beijing. It was restored in the 1950s. It's a strenuous uphill climb to the top observation post but the experience is well worth it.

The Wall is the only human made structure discernible from the Moon. It could encircle the earth in a five and a half yard wall.