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

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

An unusual round church in London with a Templar past.

A 300-year-old tea shop that brought tea to the English people, not to mention the Queen herself.

This preserved puppy was an adorable beacon of charity.

A charming 17th-century alley is lined with secondhand bookstores and antiquarian shops.

This picturesque horseshoe weir was first built in the 1600s to prevent flooding in the town of Bath.

Eighteenth-century home, where Herschel discovered the planet Uranus.

Padlocks cover this rickety footbridge with love.

Where condemned pirates met their grisly end at the gallows on the River Thames.

At this rare mosque in Tbilisi, Sunni and Shia Muslims pray side by side.

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

Most prolific publishing house in the 1600s open to the public.

Rebuilt remains of a temple to Roman god Mithras.

A 141-foot wave of crashing lumber guards the entrance to the Grand Place in Mons.

Petting this mysterious iron monkey supposedly brings good luck.

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

This singular Irish dolmen is more Frank Lloyd Wright than upright stonehenge.

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

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

The Guardian of Tallinn.

Mysteriously stacked storefront paths give this medieval British town an iconic style like none other.

The smallest pub in Britain was once a cabinet of curiosities and it still has the dead cat to prove it.

This little-known hero has been protecting "The Fens" for close to 400 years, and now from its most powerful challenger yet: climate change.