Situated in northwest Portugal where the Douro meets the Atlantic Ocean, Porto has been known around the globe as the city from which authentic Port wine has been shipped throughout the world for nearly three centuries. Rising on staggered hills along the river, this colorful city beckons you to its labyrinthine streets and stairways, medieval alleys, Baroque churches, fountains, and bell towers, Beaux-Arts buildings, and bohemian neighborhoods whose narrow cobblestoned lanes wind their way past centuries-old former merchants' homes and trendy cafés. You have a sightseeing choice today. Discover Porto by land, river and air – starting from the historic riverfront Ribeira district, walking to Vila Nova de Gaia and riding a cable car for panoramic views. Alternatively, join a local guide for a walking tour that begins in the riverside Riberia district, walking uphill to the Cathedral, crossing the top of the Luis I bridge and concluding in Vila Nova de Gaia with a view overlooking Porto. Return to ms Andorinha late morning and begin sailing to the Douro River Valley, bound for the historic port of Peso da Régua. All along the winding river, rugged conical mountains and shale hills carved by concentric vineyard terraces tell of a winemaking history that's thousands of years old. Inhospitable to most other kinds of farming, the terroir is perfect for Portugal's indigenous wine grapes, whose hardy roots can go down 30 feet or more in search of water. And since the latter half of the 17th century, when Portuguese vintners succeeded in creating a sweet fortified wine – now famous around the world as Port, named for the city of Porto – that could make the long sea voyage to Britain and other destinations without spoiling, the Douro Valley has been the only supplier of true Port, the oldest demarcated wine region on Earth.

Your choice of excursions this morning includes an opportunity to explore Pinhão and its early-20th century train station, adorned with blue-painted tiles (azulejos); or a vigorous hike in the hilltop vineyards with striking views of the town and river. Sail to Régua, where you'll have two choices; visit 18th-century Mateus Palace, a lavish Baroque residence designed by Nicolau Nasoni that is now a museum with period furnishings and artwork, a heraldic hall, formal gardens, a winery, and a chapel with tombs and reliquaries. Alternatively, join a local guide for a visit to a local wine-making estate called a quinta, rewarding with a port cocktail making class. Begin the return trip to Porto, and dock overnight in this verdant wine country, where some traditional farms grow vines on pergolas and fences so high the grapes must be harvested with ladders.