17th century streets hidden under Edinburgh were once a breeding ground for the black death.

In the heart of Luxembourg's "little Switzerland" weaves a breathtaking natural sandstone canyon with a mythological past.

An underground city of salt.

A spectacular walk on the flank of a gorge.

See replicas of Europe's most famous cave paintings and even some of the animals that feature in the art.

Home to the world's largest refracting telescope and the birthplace of modern astrophysics.

The awe-inspiring ship from the golden era of cruising has an incomparable history and a reputation as one of the world’s most haunted places.

Long before Europeans arrived, Native Americans built an artificial island out of shells that has withstood a millennia of hurricanes.

Six tiny houses built for working class people form the largest intentional cluster of Wright homes anywhere.

A fantastic example of Victorian railway engineering with two unusual decorative features.

Village situated on a narrow volcanic escarpment.

A 140-year-old castle with underground caves hidden in San Francisco.

A church of bones, decorated with 40,000 human skeletons.

A well-preserved network of cavernous tunnels have spent silent centuries removing Toronto's waste.

A network of concealed passageways lies within a busy London Underground station.

Where commuters walk through remnants of an ancient Greek necropolis.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

View the ancient remains of buildings and the ancient "River of Hades" before hopping on a train.

A tunnel that brings more than a century of history to life from the deepest parts of the Niagara Gorge.

A unique botanical garden housed in three giant geodesic domes.

The oldest hotel in the world has been operated by the same family for over 1,300 years, even catering to samurai.

Old-fashioned knowledge and modern engineering create the world's only rotating boatlift.

A 2,000-year-old computer demonstrates remarkable engineering and astronomical precision.