Hamburgers are intensely proud of their tunnel beneath the river.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

This crumbling Portuguese ruin overlooks the populace it once ruled.

A unique seaside cave where Aleister Crowley faked his own death.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

The largest catacomb system in the world.

This small chapel is built of human bones and decorated with a golden skeleton.