A hidden tunnel of bones in one of Malta's oldest churches.

The world's largest key collection features keys to the White House, Frankenstein's castle, and Hitler's bunker.

This tiny business claims to be "the smallest pub on the planet."

Chicago’s incendiary role in the labor movement.

There’s a hidden military meme engraved on the World War II Memorial.

Though they've since been renamed, these two streets hint at Dublin's darker days.

A statue honors the children who fought Nazis in Poland.

A tribute to a Ukrainian heroine who went undercover and killed several Nazi operatives.

The site of Austria's biggest concentration camp now honors its victims.

A monument to the man who almost killed Hitler.

The alleged birthplace of Lady Jane Grey, who was executed at age 16 for claiming the throne of England.

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

A blunder resulted in these charming stone-lined streams becoming the target of a Nazi bombing.

One of its engravings is believed to be among the first representations of medical and surgical instruments.

People escaping slavery may have hidden inside a corpse vault.

A curious collection of oddities including a lock of Alexander Hamilton's hair and Harry Houdini's ouija board.

A sobering scientific reminder of the human damage caused by the advent of the nuclear age.

The site of the first "historically true" UFO encounter in the U.S.

All that remains of a gigantic earth-moving machine.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

This beautiful site is where the first transatlantic telegraph was sent from.

The only substantial part of Nazi Germany's formidable defensive line through Northern Italy that survives today, largely intact.

London's only public statue of the much-married monarch adorns the gate to St Bartholomew’s Hospital.

The obelisk honors the cyclist troops who were killed during World War I.