ABOVE: PORTUGAL'S SECOND-LARGEST CITY, PORTO IS SET ON THE DOURO RIVER. ON AN ADVENTURER TOUR, PASSENGERS VISIT THE CITY THAT GAVE PORT WINE ITS NAME, SAMPLING THE RICH, FULL-BODIED REGIONAL WINES AT SANDEMAN PORT HOUSE, ESTABLISHED IN 1790.

On a cloudy day in spring, a congenial group of American vacationers on a shore excursion from the Clipper Adventurer found themselves climbing some 450 steps to enter the famed ancient abbey that rises high atop the fortified rocky islet of Mont-St.-Michel. "The pyramid of the seas," Victor Hugo called it. Heartened by intermittent flashes of sunshine and the insatiable curiosity that lures travelers from home in the first place, all huffed and puffed their way up the giant granite outcropping that soars some 300 feet above the sea. And all were rewarded not only by a time trip through the brooding old abbey buildings but sweeping views of the surrounding strand and waters, and a stretch of French countryside where Normandy meets Brittany.

One of Europe’s most compelling visitor attractions, Mont-St.-Michel is only one of the highlights of a Clipper Cruise Line itinerary irresistibly titled, "Exploring the Medieval Seaports of Western Europe."

The roster of stunning sites, each of which awaits investigation independently or via guided tour, begins with Portugal’s embarkation capital of Lisbon, followed by Leixoes, gateway to the Douro River city of Porto that gave port wine its name.

Next come stops in sun-washed Spain – first at Villagarcia for a drive through the Galacia region to visit Santiago de Compostela, after which passengers reboard at La Coruna. It’s said that more than half a million Christian pilgrims journeyed to this holy city each year during the Middle Ages, a tradition that continues today.

Then it’s Basque Country and Bilbao. I was not the only cruiser eager to see Frank Gehry’s magnificent Guggenheim Museum Bilbao that opened its highly publicized doors in 1997. The building’s daring sculptural design – a sinuous mix of limestone, glass, and gleaming titanium "fish scales" – easily upstages the museum’s collection of modern and contemporary art.

The tour, in fact, focuses on the dramatic exterior, circling the waterside creation to be sure no one overlooks the architect’s riveting integration of museum and city – including the big, busy bridge that crosses the Nervion River and pierces one side of Gehry’s structure. In comical contrast is "The Puppy," a permanent sculpted patchwork of bright seasonal blossoms that greets visitors at the museum entrance.

Along with the port of call that treats cruisers to Mont-St.-Michel, the Adventurer drops anchor in other French bastions such as Bordeaux, celebrated not only for wine production but for its 18th-century elegance. Tours that lead to nearby vineyards for tastings rank high in popularity.

On the last day at sea, the ship arrives in England’s Channel Islands, pulling into charming St. Peter Port for a look at Guernsey Island and its gorgeous gardens, towering cliffs and hidden valleys.

After each full day of on-foot explorations, the aptly-named Adventurer welcomes cruisers back aboard with an invitingly low-key and friendly ambience. The vessel’s four-deck layout means there’s no wandering with map in hand or ganging up for an elevator wait.

Indeed, with only 122 passengers and without the commotion of casinos, discos and variety shows, the ship’s style is a seamless, easygoing blend of uncrowded excursions by day and relaxation with a tasty meal and a cultural talk come evening. Passengers are supplied a nametag, and by the second or third day most are acquainted.

This year the Adventurer will cruise European waters May through July. In August the ship points toward home, lingering in Iceland, Greenland, and Atlantic Canada. In September comes a sailing from Nova Scotia to Savannah, followed by voyages to the Caribbean, South America, and the Antarctic Peninsula.

For more information, call 800/325-0010 or visit www.clippercruise.com.