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

A hands-off space for graffiti artists to hone and display their skills.

One of Antoni Gaudí’s earliest buildings, built between 1886 and 1890 for the industrialist Eusebi Güell.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

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

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

Read a book with a glass of wine at this classically restored bar.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

This restored Portuguese cafe may well be the most beautiful place in the world to grab a Big Mac.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

The world's oldest bookshop still in operation.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

The masses at this church incorporate enough moonshine and animal sacrifice that they are no longer recognizably Catholic.

This museum tucked below a charming cafe gives a brief snapshot of photographic history.

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

This silent sentry in the crypt below a large Gothic cathedral is often knee-deep in water.