This massive mural by famed pop-artist Keith Haring was hidden for almost 30 years until its 2018 rediscovery.

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

A rare tour of an aristocrat's private home reveals valuable 17th-century paintings from artists like Rembrandt.

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

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

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

A floating cat sanctuary on an Amsterdam canal.

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

This medieval castle was home to a known tyrant and features several hidden passages.

Inside this museum, visitors venture through ghost stories entrenched in Icelandic folklore.

The pioneering photographer's prints are immortalized inside her childhood home.

New York City's only radical feminist independent bookstore.

A Collegiate Gothic quadrangle that surrounds an 18th century secondary school whose financing came from the likes of Alexander Hamilton and Aaron Burr, among others.

The famed amusement district marks the beginning of summer with a wild procession of nautical creatures.

Surrounded by low rise buildings and partially converted into an auto body shop, this marble archway is the only vestige of a forgotten Manhattan estate.

Small monoliths of several varieties of stone sit alongside a wooded path in the Bronx.

A heartbreaking monument showing the last morning in the life of Jane Griffith.

Manhattan's deadly West Side railroad, which killed hundreds of New Yorkers, is remembered by this simple plaque.

A plaque immortalizes the spot where the early American spy said his famous last words: "I only regret that I have but one life to lose for my country."

The Vatican of the movie industry turned into an actual church.

A hidden architectural treasure in New York's Brooklyn.

A beautiful collection of architectural ornaments rescued from demolished New York City buildings.

One of the oldest Jewish cemeteries in the city, it is now overgrown with an urban forest.

Nature and beauty amidst pollution and industrial wreckage.