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

Abstract monuments express sorrow and resilience at the site of a horrific massacre in Nazi-occupied Serbia.

A pair of connected skyscrapers form this symbolic gateway.

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

A Serbian church lit by chandeliers made of weapons.

Structure built from the skulls of vanquished foes.

Hidden in plain sight on the Hudson River is an abandoned train station where nature has taken over.

On the Hudson resides one of the largest clocks in the world.

This evocative New Jersey statue memoralizes the Polish victims of a Soviet massacre.

One of only two commuter aerial tramways in the United States.

An alchemist's "magic door" stands in the middle of a Roman park.

New York City's smallest piece of private property.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

Resting place of Hollywood's immortals is also site of summer film screenings.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

Elevated freight railway turned wildly successful urban park.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

Manhattan’s Battery Park has a whimsical carousel full of spinning, glowing fish.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

A crumbling hospital from the 1850s on Roosevelt Island.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

Wax models of disease and deformity are on display at this German medical museum.