The only building in Louisville (hopefully) that contains two ancient holy skeletons.

Visitors to this arboretum are greeted by three smiling giants crafted from sustainable materials.

An enormous natural sandstone bridge in Kentucky.

This open air cathedral invites all faiths to worship under the only roof big enough to fit them all: the sky.

The only freestanding table rock formation east of the Mississippi.

Lions and tigers and leopards, servals, pumas, bobcats, lynxes, and ocelots... oh my!

Ruined 11th century abbey built by King David I in Edinburgh, Scotland.

This 1920s Dutch barge is now a floating bookstore.

Catacombs turned marketplace.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

The curios of pharmacist and collector Henry Wellcome.

Rebuilt remains of a temple to Roman god Mithras.

An unusual round church in London with a Templar past.

One part local history, 99 parts gruesome haunted house.

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

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

Eighty million natural history specimens call this gargantuan museum home.

Hidden beneath the streets of London is a secret subway that only carried mail.

A tongue-in-cheek arcade where the games are based on everyday life.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

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

This collection of illusory paraphernalia has been culled from the history of London's premier magician's club.

This churchyard arbor is surrounded by hundreds of gravestones placed there by author Thomas Hardy.

This shop and gallery is a modern-day cabinet of curiosities, unassumingly positioned along an urban thoroughfare.