One of the few standing Roman lighthouses and a labyrinth of tunnels are a couple of the secrets at this historic castle.

In this case, 'zero' marks the spot where the iconic Old Spanish Trail ends.

Former villa and estate of James Deering developed to preserve native tropical forests.

This stunning concert hall has become a symbol of Iceland's national recovery.

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

Once the local rulers had gone these enchanting ruins housed common folk in an almost real life fairy tale.

A quaint Russian village in the middle of a German metropolis.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

An ancient instrument used to measure the waters of the Nile so Egyptian farmers would know whether to expect famine or flood.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

Op-art architecture designed for happiness.

The burning of this 12th-century church kicked off a campaign of Norwegian Black Metal terror.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

100 year tradition of fist fights, marked by marble footsteps.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.

Once an indicator of social class, the color blue has come to define this city on the edge of the Thar Desert.

Sacred Indian temple that’s all monkey business.

One of Europe's oldest libraries.

Secret refuge and museum of the Duke of Florence.

This picturesque view of the Scottish Borders was beloved by Sir Walter Scott.

A monument celebrating the idea of reaching inaccessible places.

An 18th-century Spanish watchtower made entirely of seashell and concrete.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

The "Prussian Versailles" that is as glorious today as when it was built.