This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

Ruined castle with subterranean vaulted Goblin Ha' or "Goblin Hall."

Geodesic dome luxury retreat in the Scottish Highlands.

The one-time stronghold of the noble Douglas family, now home to ghost sightings and nesting birds.

A site of pagan worship which still attracts people looking for fairies.

A fernery hidden by neglect is uncovered, and an ancient specimen along with it.

This series of Scottish caves has no clear purpose other than baffling historians.

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

Tiny effigies of the victims of Edinburgh's famous Anatomy Murders.

A 18th century graveyard and its astonishing cortege of macabre iconography.

360° views of the city plus five floors of optical illusions and hands-on science.

One of the oldest scientific gardens in Britain, containing more than 13,302 plant species in its core collection.

This stately estate house features a tower covered in a bright, modern mural.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.

The world's oldest surviving music hall was also once a freakshow.

This stately monument has been wearing a traffic cone hat for decades much to the delight of the locals.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

The heads of two giant mythological water horses honor Scotland's horselord past.

Old-fashioned knowledge and modern engineering create the world's only rotating boatlift.

The mystery of this small, brick pond eluded its possibly only investigator until his death.

This castle was established by the 4th Duke of Montrose and is connected to the Buchanan Clan.

Railways may have forged this quintet of lovely tunnels, but now they are open to hikers.

Just a few miles from downtown Atlanta is a trail covered in a crazy collection of outsider art.

These cinderblock farmhouses were actually World War II radar stations in disguise.