Hidden beneath the streets of London is a secret subway that only carried mail.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

This locally-famous crevasse in New York State is icy all year round.

Mosaics, storks, and brothels—this ancient city has it all.

Founded as a refugee camp, now a popular tourist spot.

A German apartment building hosting as many trees as human occupants.

Beautiful carved tunnels.

Giant nude woman of Tijuana is also the artist's home.

The curios of pharmacist and collector Henry Wellcome.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

Museum dedicated to the UK's first charity for abandoned children, with keepsakes of the mothers who left them behind.

Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

When the rain falls, this drain system turns into a musical instrument.

The remains of Alfred Nobel's first nitroglycerine factory can still be found on the shores of a Swedish bay.

The second-largest (of only two in the world) large particle collider is the underdog of experimental physics.

A former poultry store that looks like a giant duck and is one of the "seven wonders" of Long Island.

An unrealized dream to wirelessly electrify the entire Earth.

An archive of nearly every day of Buckminster Fuller's life.

The world's most famous donkey lives in this pen.

From the Difference Engine to the Cray-1, all under one roof.

See the computer’s history revealed over the course of 20,000 years.

A reservoir of vintage pinball machines and arcade games for the nostalgic and thrill seeking.

A unique hanging cable-car navigates through Dresden, the oldest suspension railway in the world.

A small man-controlled waterfall powers an Art Nouveau elevator and is accessed via narrow gauge, solar-powered tramway.