The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

Locals dubbed it the "Owl Building" because of its bird-like appearance.

Turning night into day in Victorian-era Austin to thwart a serial killer.

A former electrical substation is now home to an eccentric junk art masterpiece.

Austin’s nonprofit-run graffiti park where street art is meant to be painted over.

Go inside to really appreciate this 500-year-old technological masterpiece.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

The underground sanctuary of a mysterious ancient cult.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Home to items never before seen by the public.

A grove of colossal man-made flowers built to collect the sun's rays.

One part antique store, one part curiosities hodge-podge.

Home to the largest urban bat colony in North America, estimated at 1.5 million bats.

This unique structure in suburban Austin is made up entirely of other people's castaways, and constantly changing.

A store full of vintage and indie toys designed to bring out the kid in even the crustiest of adults.

Frida Kahlo's childhood home, now a museum of her life and works.

The only castle in North America to ever house European sovereigns.

66,000 pieces of art, donated by one of the world's richest men.

Visiting this cacophonous collection of vintage novelties is like stepping into the mind of a crazed toymaker.

Superstitious? Discover the witchy side of Mexico through its largest esoteric market.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.