A forgotten "city of water" underneath the famous Trevi district.

How did a lighthouse wind up in the middle of this landlocked German city?

A triumphal steel arch on the side of a German mountain.

Blending modern art with Baroque architecture, this wondrous mosaic grotto serves as the late artist's final creation.

This painted Lego bridge is the product of over a century of locomotive history.

This futuristic German television spire is actually the world's largest digital clock.

Twisted buildings adorn the banks of the Rhine river.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

These red marks, seemingly placed at random, are in fact not.

This giant sculpture made of trash is a critique of society's wastefulness.

This oddly shaped church resembles a rocket.

Tucked away inside this concrete building is a church and its grand display of brutalist architecture.

The oldest operating roller coaster of its kind, the Montaña Suiza has been thrilling riders since 1928.

A gravity-defying "devil's bridge" that has a surprising architectural feature for its stability.

This sublime architectural marvel is a rare example of an expressionist church.

Barcelona's only remaining tram system takes riders to the Tibidabo funicular.

This home designed for chocolate magnate Antoni Amatller is an exquisite treasure-box of Catalan Modernism.

One of Antoni Gaudí's least-visited works, an homage to Catalan patrimony that mixes neo-Gothic with Modernista forms.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

This cemetery features modernist statues as strange as its name.

Mountain where Jesus was first tempted by the Devil.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

A beautiful but toxic fountain of mercury.