Maria Pía Bridge in Vila Nova de Gaia, Portugal (opens in new tab)

Porto is a city that seems engineered for wonder. Its steep cobbled streets tumble toward the Douro River, where tiled façades glow amber at sunset and old trams rattle past wine cellars older than many nations. Travelers arrive for the port wine, the melancholic strains of fado, and the dramatic riverfront skyline, but Porto’s true magic lies in the way history and industry intertwine. Few places embody that union more powerfully than the Maria Pia Bridge, a masterpiece of iron suspended abo...