Just your average Marie Antoinette–themed speakeasy in an abandoned 19th-century subway tunnel.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

A hip bar decorated with walls of golden skulls.

Order scoops of pandan, lychee, and black sesame at this family-run institution.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

The oldest family-run luncheonette in New York, last renovated in 1948, still serves food and drinks the old-fashioned way.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

La Monte Young and Marian Zazeela's "Dream House" will immerse you in an ever changing world of sound and light.

A terrific purveyor of natural history objects and curios.

The history and future of cannabis.

This historic Amsterdam bar used to accept sailor's monkeys as payment.

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

The world's only museum devoted to the wonders of fluorescence.

Famed for its pie, this eatery has a hidden tunnel that allowed Catholics to secretly walk to church during the Reformation.

This impressive collection of rare books on ancient mysticism inspired author Dan Brown.

This cheese shop also houses a museum devoted to Dutch dairy.

The world's biggest pet store.

An industrial relic is now one of Europe's most staggering art spaces.