Wadi Al-Hitan (Valley of the Whales)

A protected desert valley in the Fayoum, about three hours from Cairo, where the fossilised skeletons of ancient whales lie exposed on the surface of the sand. It became a UNESCO World Heritage Site in 2005, and it is the only place on earth where you can walk among them.

A marked trail of a few kilometres loops past the main specimens, left where they were found rather than removed to a museum. Some are near-complete and several metres long, with the vertebrae laid out in sequence and the ribcage still articulated.

What else is out here

• Fossil mangrove roots, sharks' teeth, sea turtles and sirenians in the same beds
• Wind-carved sandstone formations along the valley walls
• A small, well-made visitor centre with the best of the finds under cover
• Genuinely excellent stargazing if you camp — it is far from any town

Go in winter. There is no shade on the trail and the valley traps heat.

Forty million years ago this was the floor of the Tethys Sea, a warm shallow ocean that separated Africa from Eurasia. What is now desert was a coastal lagoon, and the animals that died in it settled into the mud and were buried.

The reason it matters

The whales here are Basilosaurus and Dorudon — fully marine animals, forty to fifty feet long, that swam and hunted like whales. And they have hind legs.

Small ones. Useless for walking, complete with knee, ankle and toes, tucked against the body. They are the vestigial remains of the four legs their ancestors used on land, and Wadi Al-Hitan preserves them better and in greater number than anywhere else in the world.

The transition from land mammal to whale was, for a long time, one of the conspicuous gaps in the fossil record — the case sceptics pointed at. This valley is where that gap was filled. The skeletons here document an animal caught in the middle of the change, and they are the reason the site is protected.

Left where they fell

The decision to conserve the fossils in place rather than excavate them is unusual and deliberate. It also makes the site fragile: the bones are exposed, and off-trail driving destroyed several specimens before access was controlled in the 2000s. Stay on the marked path, and touch nothing.