The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

The smaller of the three towers of San Marino is a former prison inaccessible from the ground level.

A maze of underground tunnels beneath one of the most beautiful forts in Serbia.

Backwards hour and minute hands and a timing mechanism that fluctuates with the temperature led to this clock tower's local nickname.

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

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

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

A museum dedicated to the former country.

A fire once nearly devoured this gorgeous 14th-century Gothic cathedral.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

This elaborately decorated, fairytale-like Romanian royal palace is one of the most striking castles in Europe.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This museum of Hawaiian and Polynesian culture is the legacy of the last descendant of the Kamehameha Dynasty.

The only royal palace on U.S. soil has been a territorial capitol, a military headquarters, and a prison for a queen.

The rotting skeleton of a shoreside fun fair that was destroyed by fire and storms still haunts the Brighton ocean view.

Half-drowned wooden stumps and stone blocks are all that remain of a Victorian landing that was destroyed by storms.

Regency-era excess on the English Coast.

Preserved baths in a Victorian-era spa town frequented by the most famous people of its day.

The bombed out remains of the old church were kept intact next to the new one, as a reminder of the futility of war.

This ruined medieval castle was the scene of Lord Robert Dudley’s seductive reception for Queen Elizabeth I.

One man's remarkable private collection of art from around the world.

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

An exquisite collection of fairytale conveyances that puts most car museums to shame.

This Taoist temple is the oldest continuously used Chinese temple in California.