An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

The oldest stone house in Paris was built by its most famous alchemist.

Notorious artist squat renovated into legal studios.

Colorful murals by Jean Cocteau hide within this peaceful London sanctuary.

Buried for centuries, this hidden cellar is all that remains of London's medieval Whitefriars Monastery.

One of the oldest remaining Catholic churches in England is home to the hand of a 7th-century saint.

The pretty iron lamp is a reminder of the architecture underneath London's streets.

Remnants of cells from the most notorious London prison may lie in the basement of a rare Victorian Gin Palace.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

This building contains a door only used by members of the royal family.

This demon atop the Notre-Dame de Paris looks utterly bored.

The celebrated eyesore created by starry-eyed sweethearts.

One of America's founding fathers lived in this London lodging between 1757 and 1775.

A relic from one of London's worst 19th-century slums.

This bookstore serves recipes from the cookbooks on sale.

The wooden telephone box hidden away in London's Piccadilly was the original prototype of the iconic kiosk.

A plaque pays tribute to the artist's longtime London home.

The first geometric self-supporting spiral stairs in Britain are a truly beautiful sight.

What started as a way to address damp basement walls turned into a house filled with intricate hand-carved designs.

This inn of the court provides a fascinating window into London’s legal and architectural history.

An agreement meant to honor the Duke of Buckingham led to this unusually-named passageway near Charing Cross.

On the eve of a condemned prisoner's death, this bell rang 12 times outside their cell.

The world's largest collection of ship figureheads includes figures from legends and history alike, from Sir Lancelot to Abraham Lincoln.

Only a few pieces remain of the structure that carried people and goods across the Thames for some 600 years.