This picturesque Umbrian city has a subterranean side that has long remained hidden.

Abandoned boats decaying in the largest ship graveyard in mainland Britain.

The last occupied troglodyte dwellings in England weren't abandoned until the 1960s.

Banksy's image of a naked man dangling from the window of a sex health clinic.

This medieval church is the only one in the world that features all Marc Chagall stained-glass windows.

One of the few remaining examples of 19th-century London’s attempt to clean up its reputation.

This Quebec estate is home to the elaborate gardens of a self-taught horticulturist.

For over 300 years this little carving has been the city’s good luck charm.

The train platform where Jews were sent to concentration camps is now preserved as a Holocaust memorial.

Vast network of air raid tunnels beneath Lombardy's capital.

Before there were doorbells this bronze ear was installed for visitors to announce their arrival.

The secret medieval communication system will whisk your words above the noise of the crowd.

Small on the outside, big on the inside, this church is an astonishing act of visual deception.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

Balconies that have a most unusual accent.

Sky ships, planes, and portraits left as unique tokens of hope and thankfulness.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

A former milk-delivery driver and his wife turn their home into a glimmering mosaic.

Artist's eccentric property excessively decorated with found objects and work of his own.

The construction of a tram line unveiled hidden remnants of the old medieval city.

A beautiful and classically designed villa, with an hourly infestation of monsters.

The mental institution where Van Gogh created some of his most famous work now allows guests to walk in the artist's footsteps.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.