A once-glowing grotto at the bottom of Waikapalae Wet Cave.

A crumbling Beaux Arts monument to the Bay Area's age of rail.

Julia Morgan's Moorish-Gothic labyrinth of fountains, trees, natural light and Oakland's notable dead.

A porcelain company's former dumping ground, completely covered in pieces of collectible ceramics.

Travelers exchange letters with woodland creatures at this mini post office.

Handmade treasures from around the world.

The last of a gourmet supermarket chain, this store helped spark California's Food Revolution.

This eatery transports diners to a place that no longer exists: East Germany.

This bakery sits on the site of the Black Panther Party's first headquarters.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

One kilometer of thick brass rod laid out before your eyes.

Plot your trip through the city on the sidewalk.

A two-inch thick solid brass rod that extends an astounding one kilometer straight into the earth.

A regular looking rock with an unbelievable history.

Mysterious 500-year-old tapestries depict a unicorn hunt.

The crown jewel of the Queens Museum is a nearly 10,000-square-foot architectural model of the city originally built for the 1964 World's Fair.

The oldest Dutch colonial stone house in New York City is a hidden gem on the border of Brooklyn and Queens.

A way to take your secrets to someone else's grave.

A restaurant on Staten Island showcases a different grandmother’s cooking every night.

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

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.

This underwater sculpture park is the basis for a manmade coral reef.

An overlooked marble is the only surviving in-place 18th century example of the measurement that changed how we define distance.

An allegorical statue of a giant pregnant woman representing justice and truth.