This massive library holds what was once the largest book collection in the world.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Underneath the bustling city streets, a hydroponic farm grows unique herbs in an urban oasis.

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

Cemetery featuring rare glass-fronted columbarium.

One of the largest pieces of scientific equipment ever carried on a NASA space shuttle sits in a Chicago alley.

An enormous park-like oasis, full of famous Chicagoans' graves.

In a quiet north Chicago neighborhood rests a stunning relic of the golden age of earthenware design.

Combination beer garden and music venue in the heart of Wicker Park.

A shining sculpture made of 3,115 lights, the number of visible stars in the Northern Hemisphere.

The 30,000-volume library is one of the world's most impressive poetry collections.

This massive stained-glass masterpiece is thought to be the largest Tiffany dome in existence.

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

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

Hidden within a Netherlands crater is a stone bed that lets those who lie in it see the sky as a curved surface.

An overgrown and largely forgotten cemetery lies hidden within the outskirts of Amsterdam.

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

A Dutch passageway's artistic, aquatic-themed makeover pays tribute to the capital city's famed waterways.

The attic of a four-century-old canal house hides a clandestine church.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

This 22-floor tower's Skydeck offers panoramic views of Amsterdam.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

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