Douro River, Porto, Portugal. Porto is one of the most beautiful cities I've had the pleasure to visit. The city is packed with cultural attractions—many of them listed as UNESCO World Heritage Sites. The port wine cellars, Oporto Cathedral, Clérigos Church Tower, and Liberdade Square are all worth exploring, yet a stroll along the Douro and dinner in a riverside cafe are singularly remarkable experiences. The river glows under the city lights at dusk.