Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

Taking the subway here means doing so over a bridge located in the middle of an estuary.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

A marvel of Byzantine engineering under the streets of Istanbul.

Over the centuries, this island paradise has done it all, from providing monks with ecclesiastical respite to sheltering an exiled Leon Trotsky.

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

An enormous public square and parade ground built to celebrate Ghana's independence.

Where thousands of slaves passed through the "Door of No Return."

This series of rope-style bridges brings visitors into a jungle layer that is usually reserved for birds and monkeys.

The Voodoo Superstore of the world.

The unique building practices of the Batammariba reflect the community's deep reverence for and connection to the earth.

This subterranean town of over 50 dwellings lies thirty feet beneath the Earth's surface.

A giant chameleon, with a fascinating purpose.

Africa's Venice on stilts.

A striking symbol of the Bulgarian capital.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

This historic black and white monastery is one of Bulgaria's architectural jewels.

The best-preserved example of a unique structure in Nubian architecture.

Crumbling pyramids and temple ruins stand within the shadow of this sacred butte.

These Nubian pyramids are strange and unique, even by pyramid standards.

The largest camel market in West Africa

Thousands of colorful pirogues showcase ingenious craftsmanship at the largest fishermen port in Nouakchott.

Five ancient libraries, little changed for centuries, preserve a medieval archive of Quranic lore and civic documents

An architectural relic that survived the hands of time.