Douro River

The Other Wines: Although famous for Port, the Douro Valley produces regular wines, too — both reds and whites, many from old Portuguese varietal vines. On a hot day, it's hard to beat a glass of crisp, slightly fizzy “vinho verde.”

The Locks: Dams aid navigation on the Douro, and you'll travel through impressive locks that are up to 100 feet deep.

Port: A Douro itinerary offers plenty of opportunities to taste this fortified wine in all its versions, at Vila Nova de Gaia's port "lodges" (warehouses across the river from Porto) and at “quintas” (wineries) along the river.

Gorgeous Scenery: Vineyards rise to astonishing heights along the deep Douro Valley, offering spectacular views during excursions. Toward the Spanish border, the terrain turns rocky and rugged, but is equally stunning.

Porto: In this UNESCO-designated city, tear yourself away from port tastings (don't miss Taylor's) long enough to see the Bolsa Palace, Clérigos Tower, Livraria Lello bookstore (a former J.K. Rowling haunt), and the lively, restaurant-lined quay.

Salamanca: This city of golden sandstone buildings — also UNESCO-designated — is famous as the home of the oldest university in Spain (established in 1218), where Christopher Columbus studied. It's worth the long bus transfer.

Régua: Visit the wine museum or take an excursion to the splendid 18th-century Mateus Palace and its gardens.

Expect Long Bus Rides: Most attractions are off the river, requiring schleps of 45 minutes to two hours.

No Night Cruising: Only daytime navigation is allowed, so you'll spend a fair amount of time on board.