Hidden behind West Philadelphia rowhomes is a haven for migratory and local bird species both ordinary and rare.

The world's third-largest crystal sphere has sat in the Penn Museum since 1927 with the exception of one outlandish theft.

This little-known Revolutionary War fort is supposedly haunted by the ghosts of its past.

In the early 1800s, surgery was also a show.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.

Mural made of 100,000 pieces of hand blown glass, and until recently, the largest glass mural in the US.

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

This ornate Victorian marketplace was the setting for Diagon Alley and the Leaky Cauldron in the Harry Potter films.

The world's oldest hologram gallery and the labyrinthine laser laboratory of a holography pioneer.

A DIY art gallery/music venue/lecture hall dedicated to video game culture.

The feral felines of Roosevelt Island have a small army of allies and an abandoned hospital all to themselves.

A semi-scholarly approach to sex.

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

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

Several times a year, during low tide, two pairs of historic train tracks are revealed on this New Jersey beach.

A world-class collection of mechanical musical instruments and automata.

Destructive children, start your engines.

A reservoir of vintage pinball machines and arcade games for the nostalgic and thrill seeking.

A unique sculpture park that specializes in the huge and bizarre.

Instruments, apparatus, and rare books all relating to chemistry and its related sciences.

Huge masonic hall in Philadelphia with lavishly themed rooms.

About as hidden as can be, this specialty coffee shop is wedged between multi-story buildings at the end of a dark, skinny alleyway in Seoul.

One man's lifetime collection of tiny objects of wisdom gathered from around the world, on display for public enjoyment.