A collision of human error and natural geothermal pressure created this rainbow-colored geologic wonder.

A kaleidoscopic warehouse-maze of handmade neon signs.

A magical place that lets you play in and explore the world of Studio Ghibli.

The macabre collection of Jacques Sirgent, an expert scholar on the undead and all of their trappings.

This iconic L.A. bookshop is housed in an abandoned bank—both symbolic and chic.

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

A psychedelic labyrinth on the San Francisco bay.

An artsy hidden staircase leads to breathtaking views of San Francisco.

A terrific purveyor of natural history objects and curios.

During prohibition, corrupt city officials ran drinking dens under the streets of Downtown Los Angeles.

A sprawling outdoor museum filled with larger-than-life works of art.

What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

A place to eat for on-the-run agents and espionage enthusiasts.

This surprising gem is a world-class archeological museum hidden at the University of Chicago.

Complex aquaponics systems allow fish and plants to grow in harmony.

An off-the-beaten-path place to literally hang beneath Milwaukee's Holton Street Bridge.

This tiny historic jail along Route 66 is the perfect fit for exactly one criminal and their partner-in-crime.

An unassuming store hides relics of its former life as the jazz club that hosted some of the best black performers of the 1920s and '30s.

Years of archaeology, just chillin' by the water cooler.

Fragments of architectural wonders from around the globe are embedded in the newspaper building's walls.

A little-known subterranean street runs under some of the best-known buildings in Chicago's River North.

One-of-a-kind preserved ruins of an abandoned 1880s church in Chicago's Pilsen neighborhood.

All of Chicago's wood-paved streets are long gone but two alleys remain.

A century-old network of freight tunnels underneath the city's historic business district.