Poseidon? No one seems to know.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

This graffitied 19th-century building was a prototype of European industrial architecture.

A Byzantine-era church hidden in a wooded area below the Acropolis.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

The oldest standing Byzantine church in Athens is tucked within a monastery in the middle of an upscale shopping district.

Graffiti from the 16th and 17th centuries cover the walls of this part of the Tower of London.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The television series' iconic giant foot was borrowed from this classical painting.

An alleyway plaque is all that remains of the independent Texas' envoy that forgot to pay their rent for over a century.

This unassuming alcove in London’s famous Tower Bridge once served to capture, store, and display dead bodies from the River Thames.

A haunting painting meant to capture the calamity of World War I.

This sculpture, residing in a quiet corner of a London park, honors the victims of 9/11.

These marks in Myddelton Passage aren't your run-of-the-mill vandalism, and they weren't made by your typical vandal.

This magnificently macabre shield shows the power of chivalrous love in medieval times.

The famous polar explorer stands outside the Royal Geographical Society's headquarters.

Legend has it that seven Anglo-Saxon kings were coronated on this stone, located in the appropriately-named town of Kingston.

A mysterious shape catches the eye in this 16th-century painting.

This may be the last of London's wooden pavements, which were once a common sight in the city.

This bewitching Babylonian goddess haunts a hallway of the British Museum.

This mysterious and unique painting is filled with symbolism.

A domino effect created with Britain’s iconic telephone boxes.

This macabre painting of a Shakespearean scene looks like something out of a nightmare.

This open-air mosaic gallery honoring an English artist took hundreds of volunteers more than seven years to create.