The same water that fills a luxury resort’s pools feeds these free hot springs in the rainforest.

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

The bronze uniforms commemorate the vital role of women during World War II.

The commemorative stone column conceals a secret laboratory.

An architectural oddity hides in plain sight on this iconic London bridge.

This unique bridge curls up like a caterpillar to let boats pass and then unfurls again to span a small canal.

London's last remaining public soapbox site has seen speeches from Karl Marx, Vladmir Lenin, and George Orwell.

Hear the quietest sound from across the dome.

An unusual round church in London with a Templar past.

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

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

Engineering ingenuity during the battle of Gibraltar.

Single runway interrupted by a busy road that cuts across its middle.

Frequent fliers welcome in this airplane hotel.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

This influential Renaissance-era library was once the haunt of kings and monks.

This little sun pays homage to a massive gate that once stood at this location.

An ancient Egyptian temple in the middle of Madrid, Spain.

Madrid's romantically ornate crystal palace has been offering shelter to plants and art for over a century.

A 16th-century Andalusian palace.

The world's largest wooden structure.

The final resting place of the great navigator, or maybe his brother.

Spanish architects used seized Muslim gravestones to rebuild parts of the fortress.