The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

This luxury shopping lane has been protected by its own tiny police force for over a century.

This hidden green space is the city's second largest conservatory.

Eighty million natural history specimens call this gargantuan museum home.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

The curios of pharmacist and collector Henry Wellcome.

An unusual round church in London with a Templar past.

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

The longest fence in the world stretches over 3,000 miles to keep the dingoes out.

The largest collection of Indigenous Australian artifacts in the world, and the rare museum where wood-and-glass cabinets have trumped interactive exhibits.

An opal mining town in the middle of Australia where people live, worship, and shop underground.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

On a small Puerto Rican island, banks of secret naval bunkers lie abandoned and filled with piles of office equipment.