Porto's Douro waterfront carries 2,000 years of commerce under six iron and stone arches built between 1806 and 2003. The oldest, Ponte das Barcas, floated on pontoons until Napoleon's army crossed in 1809; the newest, Ponte do Infante, cantilevered 280 metres without mid-river support when engineers opened it for European Capital of Culture year. Between them lies the architectural lineage of 19th-century engineering — Gustave Eiffel's protégé Théophile Seyrig designed Ponte Luís I's twin-deck iron lattice in 1886, a 395-metre span that still carries metro trains on its upper tier and road traffic 45 metres below. The six bridges cruise porto sunset route departs from Cais da Ribeira, where medieval wine cellars drop straight into the river. Standard 50-minute departures run hourly between 10:00 and 18:00, with late-afternoon sailings timed to catch westward light as the boat passes under Dom Luís I, Ponte da Arrábida's 1963 concrete arch (then the world's longest), and the cable-stayed asymmetry of Ponte da Arrábida. UNESCO listed the Douro valley in 2001 for its terraced vineyards and hydraulic port-wine trade infrastructure; the river corridor through Porto itself remains a working freight channel, with rabelo boats now converted to tour vessels instead of hauling casks from Régua. Evening light transforms the north-bank warren of azulejo-tiled facades and the south-bank port lodges — Sandeman, Taylor's, Graham's — into a study of ochre and shadow. The route passes all six spans in chronological order, turning at Ponte do Freixo before the tidal estuary widens. Departures from 16:30 onward offer the clearest sunset angles, with the sun descending behind Vila Nova de Gaia's ridge between late September and March. The standard adult fare holds at €18 for the 50-minute circuit, with optional extensions including port-cellar tastings docked at Graham's or Cálem after the return to Ribeira. Operators launch from the same quay where 18th-century British wine factors loaded barrels bound for London and Bristol.