Cairo in $640s-$740s RT

Cairo is one of those places with a deep, almost tangible sense of history. Under the shadow of the ancient Great Pyramids, Roman ruins stand side by side with stately Islamic architecture, evidence of the varied cultures that have called the city home.

Some relics, however, raise more questions than answers.

Head to the second floor of the Egyptian Museum, and you'll find the collection's most enduring mystery: the Sabu disk. Shaped like a wide, shallow bowl with carefully carved lobes, this 5,000-year-old sandstone artifact looks almost like a hubcap or a steering wheel. Its purpose? Completely unknown.

The current mainstream theory says the Sabu disk was used to hold oil for ceremonies. But the most fun theory is that it was some kind of ancient flywheel, left behind by a UFO centuries ago.

If you come up with your own hypothesis on your trip to Cairo, send us a postcard! And while you're at the museum, don't forget to check out this toy bird that looks suspiciously like an airplane...