Tubing through a cave lit with glowworms is a magical underground experience.

An uber-secure, windowless tower of doom in the center of Manhattan is an NSA spyscraper.

This plot of old-growth forest is the largest surviving remnant of New York City's original woodland.

This jaw-dropping 19th-century bridge uses its reflection to form what appears to be a perfect circle.

The ancient tomb acts as a calendar that keeps perfect time.

A tiny microvalley etched into the side of Knocknarea Mountain hides another world.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A hugely vast Irish landscape of barren rock that stretches for miles.

This single room has survived the centuries with almost no deterioration.

A proud bronze billy stands as an eternal symbol of Ireland's oldest festival, where a goat is made king.

An abandoned faux-pub made famous by a Guinness commercial.

An Irish town has built a statue to a silent film actor simply thanks to the holidays he once spent there.

Just a few miles off the western coast of Ireland lies an isle steeped in Irish literary history.

Perfectly preserved ancient monastery in an impossibly dramatic location on a rocky island in the Atlantic.

A spiral staircase twists to the top of this unusual Czech lookout tower.

This sword isn't waiting for a king to pull it out. It was placed there by a saint.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

Sculpture of a legendary French dragon.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A Franco-era dam flooded (almost) everyone out of this centuries-old Aragonese town.

On the Oregon coast there is a natural hole that seems to be draining the sea.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.

Prove you deserve to be fed by Kenny Shopsin.