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

Eighty million natural history specimens call this gargantuan museum home.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

Featured in one of the most iconic scenes in cinema history.

The haunting complex honors the millions of Ukrainians who died in the forced famine under Soviet rule.

A reconstructed medieval gateway that was the magnificent entrance to the capital city dating back to 1037.

A preposterously luxurious hotel with gold-plated iPads, Rolls Royce chauffeurs, and a staff that trains by watching "Downton Abbey."

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

Taking the subway here means doing so over a bridge located in the middle of an estuary.

Ancient serpentine sacrifice holder that has stood the test of time.

A fountain standing as a testament to a doomed alliance.

This half-forgotten fortress was constructed by the Ottoman conqueror of Constantinople.

The most metal church of all time was built in record time because of an international, pious pissing contest.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

A marvel of Byzantine engineering under the streets of Istanbul.

The bears of Bern have been a city highlight for over 500 years.

It is said that each of the white stones in the red facade of this medieval house represents the head of a murdered Swedish noble.

It houses the remains of a 17th-century version of the Titanic.

Once the grandest synagogue in medieval Spain, it now stands as a memorial of the 15th-century Jewish exile.

Arguably the most striking example of street art in Tarragona

Touching the iron railings of Tarragona's balcony to the Mediterranean is said to bring good luck.

Long tunnels run under the ancient chariot racing circuit to the tower.

This Roman arena once played host to bloody gladiatorial battles.

Stunning Roman aqueduct used for 1900 years and still standing.