Cross the lower deck of the bridge and you're in Vila Nova de Gaia, a separate city, where the lodges that give port its name line the riverbank. Until 1986 port could only be exported from here, which is why the big English and Portuguese houses all built their warehouses in Gaia: the wine came down the Douro from the vineyards on the rabelo barges, aged in cool lodges near the sea, and left from the quay. Today the wine arrives by tanker truck, but the lodges are still where it matures.
Pick two lodges, not five. Cálem sits right on the riverfront and combines a small museum with a short tour and tasting, easy to fit in if you're tired. Taylor's sits uphill on Rua do Choupelo, with a terrace over the river, an audio-guided cellar tour in 13 languages and a cellar open from 10:00 to 18:15 daily. Graham's 1890 Lodge, a little further along the hillside, offers a guided tour with food pairings. Honest verdict: most tours repeat the same history, and the tasting is the real reason to go. Skip the cheapest generic tours with a single shot; a flight of three styles teaches you more.
Port is a fortified wine from the Douro: fermentation is stopped with a grape spirit, which leaves it sweet and strong at 19-22% alcohol. The styles to learn are ruby (young, red fruit, aged in tanks), tawny (aged in wood, nutty and amber, usually the one people end up loving), white (dry to sweet, often served chilled), and vintage (declared only in the best years, aged for decades in bottle). LBV (late bottled vintage) is the middle ground.