High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

For more than a century, revolutionary graffiti has marked the wall of a Parisian church.

A series of abstract, silly sculptures represent the works of a great modern classical composer.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

The spiral staircase hidden inside this giant Parisian column was likely built for Catherine de Medici's astrologer.

Executions were once held near this beautiful 18th-century fountain.

Noirish green neon marks the location of one of the oldest private detective agencies in France.

This small, ingenious cannon once helped regulate Parisian life.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

The first green space constructed on an elevated viaduct.

With no menu and no sign, this 130-year-old taverna doles out affordable home cooking.

The ruined doorway is a portal to the building's turbulent and torturous past.

An ancient octagonal weather station named for the eight Greek gods of wind.

These ancient ruins hide in plain sight next to a dessert shop.

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

The only surviving choragic monument is a trophy awarded in 334 BC for the winning dramatic chorus.

A Byzantine church containing the holy remnants of three saints sits atop the site of an ancient temple.

The home of Greece’s national poet sits crumbling in the middle of a popular tourist district.

This building displays the scars of the “Dekemvriana,” a dark time in modern Greek history.

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

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

This abandoned shopping arcade has new life as an art installation.

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

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