This symbol of Polish heritage survived the occupation during World War II, hidden in plain sight.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

A hidden art gallery in an abandoned Warsaw fort.

Warsaw's fantastically preserved gasworks...almost.

A program of Communist glamour in post-Stalin Poland is preserved in this colorful museum.

The final resting place of more than 200,000 people, this is one of the largest cemeteries in Europe.

The last king of Poland was interred in this church nearly 200 years after his death.

The Polish capital has had a deep connection to its guardian mermaid for almost a millennium now.

A menacing statue of this mythical creature can be seen at the legendary site of the monster's lair.

A statue honors the children who fought Nazis in Poland.

A tribute to the Polish insurgents who fought in the failed attempt to end their city's Nazi occupation.

The world’s narrowest house makes for an awkward, four-foot-wide living space.

Order “Proletariat’s Cutlet” at this communist-themed restaurant allegedly once visited by Lenin.

This hidden collection of everyday objects illustrates life within communist Poland.

Hundreds of notes give thanks to the patron saint of lost causes.

After the famous composer died in Paris, his sister snuck his heart out of the country to honor his wish that it be buried in their native country.

One of the world's largest collections of medieval religious art.

Legend says that this short Canadian tunnel still holds the dying screams of a girl who burned alive.

A Canadian POW for German soldiers during WWII where prisoners hatched an elaborate escape plan.

This bomb shelter-themed bar has barely changed since it opened.

The largest natural travertine bridge in the world is nestled in a small canyon in central Arizona.

This 40-room dwelling tucked within a cliff was built by the basin's prehistoric residents.

An abandoned facility that has become a place of ritualistic satanic worship, or so rumor has it.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.