Nabta Playa: A mysterious stone circle that may be the world's oldest astronomical observatory

Name: Nabta Playa

What it is: An ancient stone circle in the Egyptian desert that may be the oldest known astronomical observatory

Where it is from: An desert area of southern Egypt, about 175 miles (280 kilometers) southwest of Aswan, that was once inhabited by the ancient Nubians

When it was made: About 7,500 years ago

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What it tells us about the past: Nabta Playa, which is 2,000 years older than Stonehenge, may have been one of the earliest astronomical observatories.

Today, its main stones are in a museum in Aswan to protect them from vandalism. But originally, Nabta Playa consisted of dozens of upright stones, each a few feet high, in the desert about 60 miles (100 km) west of the Nile.