Want to taste the world's best (and rarest) beer? Then you'd better get in line early.

It was a quest for the holy grail of beers, the legendary brews of the remote Belgian Trappist abbey of Saint Sixtus. Searching the west Flanders platteland, we drove through countryside so flat the mountains of harvested sugar beets provided the only topographic relief. A dome of low, gray clouds hung overhead as we bumbled down farm lanes and allées, seemingly forever thwarted.

With more than 500 different kinds of beers, Belgians enjoy one of the world's great brewing traditions. The country's 100-plus breweries produce an array of styles: wild-yeasted lambics and cherry-tinged krieks, Belgian pale ales and oudbruin brown ones, lively witbiers, Flanders' crisp golden Duvel (named after the devil), Wallonia's intriguing and unpredictable saisons.

But above all these beers, it's the ales of the six Belgian Trappist monasteries that have captivated beer aficionados worldwide.­ And these connoisseurs have canonized the smallest and most isolated monastery of the bunch, Saint Sixtus, as the finest Trappist brewery of all, hailing the monks' rich, impossibly complex Westvleteren 12 as the best - and rarest - beer on earth.

The Spartans of the monastery movement, Trappists adhere to an austere cloistered regimen that requires self-sufficiency and manual labor. They founded Saint ­Sixtus in 1831, and by 1836 they were brewing beer that garnered renown. But in 1945, the monks made a momentous decision: They would no longer sell commercially. To focus on spiritual matters, the monks decided to limit their sales to the abbey and the nearby In de Vrede café, which remain the only authorized sources of Westvleteren beer. "[It's] the most famous beer in Belgium," says Michael Jackson, famous British beer maven and author of The Great Beers of Belgium.

Ironically, our long, looping hunt for serene Saint Sixtus took us past the great battlefield of Waterloo and omnipresent reminders of World War I, including Ypres - the epicenter of WWI's bloody trench warfare, memorialized forever in the sobering In Flanders Fields Museum. Thousands of British soldiers found respite in nearby Poperinge's Talbot House, which remains a stirring museum. Poperinge is also the capital of Hoppeland, a region of towering ­poles that the hops climb to yield beer's traditional preserving and flavoring ingredient. When we saw the hop gardens and signs for Abdij Sint-Sixtus, I knew we were getting close.

We headed down a macadam lane through small villages and checkerboard fields mounded with rugby-ball-sized root crops. Coppices of trees punctuated the landscape. Couples in wool caps and head scarves walked the road. Traffic picked up. A file of slender bicyclists sped by. I suddenly caught a dash of color in the gray, mottled sky - a covey of five hang gliders swooping down on Technicolor pterodactyl wings.

In the distance, I spotted a low-slung fieldstone building with a large parking lot. The cyclists veered in. As we drew closer, the old abbey came into view, as stolid and resolute as faith itself. The hang-gliders dipped their wings and swept across the sky, crisscrossing the road as they slowly came to earth. As the first hang glider landed beside the fieldstone building, I finally realized that they, too, were dropping in for a beer.

The In de Vrede café was a cheery redoubt of beer fanciers. The slender cyclists turned out to be elderly guys in blue spandex waving at the waitress, as did the wind-bussed glider pilots who clomped in after us. A family of round Belgians with red cheeks sat happily hoisting goblets of dark beer. A table of British beer enthusiasts from the red double-decker bus in the parking lot compared tasting notes.