This steel frame is a skeletal mirage of a lost 16th-century stone building.

Home to the world's oldest functioning orrery.

This vast collection of smoking pipes from across the world spans centuries.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

A beautifully eclectic mix of architectural styles.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A market built atop boats is one of the few floating holiday markets in Europe.

The attic of a four-century-old canal house hides a clandestine church.

Chicago’s incendiary role in the labor movement.

An Amsterdam street lined with antique shops each one dedicated to a different obscure collection.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

Three connected pink triangles memorialize persecuted gays and lesbians throughout history.

One of the largest, oldest, darkest, quietest motel rooms in the world.

The installation’s official name, “You Who Are Getting Obliterated in the Dancing Swarm of Fireflies,” says it all.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

In a 345-million-year-old cave that's 200 feet underground, dinner awaits.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

Oh, just a motel on the edge of the desert decorated with thousands of clowns conveniently located next to an abandoned graveyard.

A sculptural commentary on capitalism pokes up from the East River.

A living archive of urban activism and space reclaimed.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.

This tiny, painted door at the base of a tree stump has been a fixture of the Harvard University campus for decades.

The thousands of shades on display — some toxic, others impossibly rare — are a library of more than just color.

A museum of carnival attractions where you are invited to ride the rides.