Wedged between two buildings at the Great Ormond Street Hospital is this secret music installation.

The largest of London's subterranean rivers and once a mad, bad center of London life.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

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

This London pub hides a peculiar secret: a recreation of the rooms shared at 221b Baker Street by Sherlock Holmes and Dr. Watson.

A hands-off space for graffiti artists to hone and display their skills.

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

An unusual round church in London with a Templar past.

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

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

A 30-acre garden inspired by the principles of modern physics.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

This South London cemetery holds the remains of more than 15,000 people.

Northern Ireland's Brobdingnagian stepping stones.

The atmospheric road was never meant to be so creepy.

The world's largest collection of witchcraft regalia.

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

These fantastically named natural pools look like something out of a Scottish myth.

A small literary museum remembers the life and works of the author of The Thirty-Nine Steps.

A stone plaque and a winking pub name are all that remain to remember the victims of deadly 1836 avalanche.

Overlooking a Scottish loch, this beautifully crumbling castle once inspired a poem by William Wordsworth.

Thanks to both terrific preservation and historic vandalism this ancient site is known as the "Heart of Neolithic Orkney."

The strange behavior of a tween led to allegations of witchcraft and a curse being placed on anybody within earshot.

A rotating bridge that carries a little canal over a larger one.