A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

This museum sits on the site of a decommissioned military communications base.

A former special storage facility for documents during the Cold War.

Once the future of underwater combat, this old sub is now open for visitors to muck around in.

One of the oldest bank museums in Europe showcases unusual currencies of the world and other money-related miscellanea.

Losing lottery tickets are deposited at this shrine in hopes of better luck.

Centuries of warfare, tragedy, executions, and poetry come together in this 13th-century fortress.

A collection of housewares from recent Irish history adjoined by a tower from ancient Irish history.

A Victorian marvel of engineering is now a 21st-century tourist attraction.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

1513 Turkish world map, full of European state secrets and snarky commentary.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

This medieval manor house was equipped with secret compartments for hiding priests.

A surprising and unconventional mosque hidden in the subsoil of Istanbul.

The legendary luxury train passage is commemorated with a charming museum inside its former eastern terminus.

This former Imperial summer home was the venue for a royal slap that once echoed 'round the world.

A fountain standing as a testament to a doomed alliance.

A sixth-century Byzantine cistern hidden below a modern carpet store.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

A relic of the Cold War tucked away in the forested hills above Bratislava.

38-story baroque tower reflecting Detroit's rise, fall, and possible rise again.

Detroit’s downtown castle is one of the oldest structures in the city.

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