Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

An ethereal glowing blue ocean cave in Croatia.

The stunning interior of this Gothic church is covered in ornate gold details.

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

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

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

A towering spire in the fortress of Kalemegdan honors the victorious armies of Serbia during their struggles against the Ottoman Empire.

In the hinterlands of Serbia's capital, a giant reflective mushroom houses an aeronautical history of the former Yugoslav republic.

Destroyed Serbian army headquarters sits half crumbled in a largely revitalized Belgrade.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

The bunker where Hitler took his own life is hidden under this deliberately ordinary parking lot.

An abandoned NSA listening post on Berlin's "Devil's Mountain."

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

A whimsical and twisted animatronic monster tour beneath the streets of Berlin.

Strolling through these vintage locomotives offers a surprising amount of insight into the history of Kenya.

Rusting railcars and locomotive equipment fill this Ethiopian train graveyard.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

A labor of love and aviation in Nigeria.

This modern museum of Mediterranean culture is surrounded by a surreal concrete honeycomb.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

This building holds the embalmed remains of the leader of the Bolshevik Revolution.

The Uros people live on floating reed islands in lake Titicaca.

A strangely forgotten claimant to the much contested title of "Source of the Nile."