These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

This macabre masterpiece of a mural is one of Francisco Goya's "Black Paintings."

The partially submerged ruins of a white marble quarry used in ancient Greece for over 1,200 years.

This once architecturally advanced housing complex is now a haven for squatters that still bears the scars of war.

This beehive tomb built for royalty sat hidden for over 3,000 years.

These ruins of a sacred Ancient Greek temple stand next to a luxurious modern resort.

An inconspicuous suburban street corner is the site of San Diego's worst air disaster.

This pink watchtower served as the seat of the Greek government after independence from the Turks.

The nuns here cultivate silk to weave some of the finest scarves in the world.

Built by the Ancient Greeks, this chariot bridge is still in use today.

A crushed gate and giant bronze head serve as a reminder of Greece's fight for freedom.

A small park on Bourbon Street features life-size bronze statues of New Orleans musicians.

The ruins of an ancient Roman tomb hidden in the basement of a trendy clothing store.

Scars of this building's past life as a violent prison still cover its walls.

The site where hundreds of Greeks were tortured by the Nazi secret police is now a cosmetics store.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

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

Overlooking the harbor is a beautiful neglected mansion guarded by two Egyptian sphinxes.

This chapel on a cliff is renowned for its healing powers and was founded on the site of a supposed divine intervention.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

A man's head is enshrined beneath a statue near the first building constructed for the modern Olympic Games.

The Cycladic architecture makes this Athens neighborhood feel like an island paradise hidden in the shadow of the Acropolis.

The factory for the popular Dumbo location, the Greenpoint shop is a quiet gem.