The Tagus estuary has carried explorers, traders, and exiles for three millennia. When Vasco da Gama departed in 1497, his four ships slipped past the same limestone bluffs that frame today's waterfront, bound for India with a crew who would not see Lisbon again for two years. The river is Europe's longest, stretching 1,038 kilometres from the Serra de Albarracín to the Atlantic, but its final seven-kilometre reach through Lisbon remains its most storied. Phoenicians anchored here; Romans built wharves; Moorish dhows unloaded spices on quays that would later witness caravels returning with gold, ivory, and cartographic secrets that redrew the world. A Lisbon boat ride today traces that imperial waterfront in reverse. The Padrão dos Descobrimentos monument rises 52 metres on the Belém shore, its stone prow angled toward open ocean, carved figures of Henry the Navigator and his cartographers frozen mid-voyage. Upstream, the 25 de Abril suspension bridge spans 2,277 metres, its red steel towers echoing San Francisco's Golden Gate—both designed by the American Bridge Company within three decades of each other. Beneath it, the Cristo Rei statue watches from the southern bank, arms outstretched over the narrowest crossing point, erected in 1959 as a thanks offering after Portugal avoided the Second World War. The Belém Tower, built in 1519 as a fortress guarding the river mouth, now stands marooned by centuries of silt accumulation, its Manueline stonework—rope motifs, armillary spheres—still sharp in afternoon light. Tagus River cruises operate daily from the Estação Fluvial Sul e Sueste terminal on Avenida Infante Dom Henrique, the same pier where packet steamers once disembarked passengers from Africa and Brazil. Standard sightseeing sailings depart every hour between 09:00 and 19:00, with sunset departures timed to the season's golden hour. Some vessels carry audio guides in eight languages; others offer open bars and live DJs transforming the waterway into a floating club. The estuary's width—up to 15 kilometres at its broadest—means even peak-season cruises feel uncrowded, the city's seven hills receding into haze as you drift past container terminals, dry docks, and the occasional tall ship moored for restoration.