One of the "twins" in these falls on the Snake River was sacrificed for hydropower generation in the 1930s.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This limestone cave offers an incredible view of the Río Grande de Arecibo valley.

Rusting, graffiti-covered tanks litter the beach of this island, once used by the U.S. military for target practice.

The world's brightest bioluminescent bay.

This picturesque horseshoe weir was first built in the 1600s to prevent flooding in the town of Bath.

This astronomical clock is the second oldest in England.

The largest of only eight working transporter bridges left in the world.

This striking steel sculpture transforms environmental data into art.

Named after a lodging site that existed nearby, a bridge has existed at this location since 1455.

Local legend says Isaac Newton built this footbridge without any screws, bolts, or nails.

These mysterious Viking chess pieces spent centuries hidden on a remote Scottish island.

Scattered throughout London are ancient remnants of the city's former bounding wall.

Its collection includes a broad array of social, geographic, graphic design, and political history.

The Great Fire of London and the regulation of one-way streets both started in this alley.

The commemorative stone column conceals a secret laboratory.

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

These wire animal sculptures commemorate the exotic inhabitants that once called the Tower of London home.

Tucked away in the Tower of London is the weapon once used to execute high-profile prisoners.

This ancient Egyptian obelisk still bears the wounds of World War I.

A statue of the legendary Celtic warrior queen who fought the Roman invaders stands in one of the cities she once destroyed.

The Florence Nightingale Museum is home to the famous nurse's most treasured possession: her beloved pet owl.

The beloved beast's taxidermy remains sit in the Natural History Museum's cafe.

The bones of two medieval royal lions were discovered at the historic fortress.