A 140-year-old castle with underground caves hidden in San Francisco.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

An artsy hidden staircase leads to breathtaking views of San Francisco.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

Edinburgh’s version of the Sistine Chapel is this former church, with an interior covered in paintings done by one woman over the course of nearly a decade.

Inside this cathedral is a shoulder bone belonging to the Patron Saint of Scotland.

A former telephone box found new life as a photo booth and charity fundraiser.

This stately bank building hides a spectacular star-studded ceiling.

This extraordinary Viking artifact has traveled throughout the city.

One of Edinburgh's oldest pubs hides a 19th-century skittles alley in the back.

The most loyal of little dogs, or a Victorian era publicity stunt?

A sweet symbol marks the place where torturous executions were once carried out.

An American ghost town hides along a side street in Scotland's capital.

Near the former site of numerous witch burnings, this lavish Edinburgh mainstay pays homage to Scotland's brutal history.

If you fly into Edinburgh Airport, it's possible to spot this prehistoric site without even getting off the plane.

This extinct volcano rises above Edinburgh and is special for its panoramic views over the city.

One of Edinburgh's most popular works of street art is located well off the beaten path.

Neon artworks light up this dark Edinburgh tunnel.

An iconic red telephone box turned tiny art gallery.

An artist's whimsical transformation of everyday objects.

This former train tunnel is filled with lines from a poem crafted by Robert Louis Stevenson.

Enter this small nook and you'll be surrounded by 360 degrees of street art.

This king penguin is a knighted brigadier of the Norwegian Army.

Anonymously sculpted and donated, these sculptures made from poetry books and pages are sprinkled around the city.