Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

This statue honors the thousands of Allied avians that served and died for France during World War I.

An underground city of ancient quarry tunnels hid thousands of Allied soldiers in WWI.

This stunning French estate was so lavish that it landed its original owner in jail for the rest of his life.

A monument to the thousands of Canadian soldiers who died capturing the French ridge during World War I.

The 16th-century church was kept in its ruined state as a reminder of the casualties of World War I.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

A lush indoor jungle fills this bustling Madrid transportation hub.

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

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Thanks to modern navigational tools we now know that the true prime meridian runs through a park next door.