The attic of a four-century-old canal house hides a clandestine church.

A floating cat sanctuary on an Amsterdam canal.

The world's only museum devoted to the wonders of fluorescence.

Hundreds of huge, centuries-old horseshoes adorn the walls of this nontraditional 12th-century castle.

Isaac Newton's former home, where the famous apple tree still stands.

The castle still holds traces of the abandoned Roman fort it was built atop.

Recently restored menagerie of Victorian-era beasts.

A harem-inspired Moorish fantasy design in a Victorian-era Welsh castle.

Brass bricks outline the locations of Edinburgh's lost, lively market stalls.

Edinburgh's oldest statue hides within a parking lot behind the city's iconic cathedral.

The Scottish Reformation leader's grave was paved over and is now a parking lot.

A pair of stones embedded in an Edinburgh street memorialize one of the city's last public hangings.

The 20th-century chapel’s intricate woodwork includes amazing details, most notably angels playing bagpipes.

This alley off Edinburgh's Royal Mile contains remnants of the city's seedier history.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

This otherwise ordinary close on the Royal Mile constituted the end of the world for Edinburgh’s poorest residents.

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

Protecting the dead from opportunistic body snatchers.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

This short bridge is the only thing connecting a tiny Irish island to the mainland.

Northern Ireland's Brobdingnagian stepping stones.

An artificial date palm stands as a memorial to Warsaw's Jewish community.

In the summer, the area around this sculpture transforms into a vibrant concert venue.

Special benches that play Chopin's music are scattered throughout his native city.