As beer recaptures its former glory, beer tourism has become an emerging phenomenon. People want to taste beers in their natural habitat. They want to see the breweries, drink in the beer halls, and eat the local food. I was at a lambic-beer festival in Belgium recently, and the tents were full of Americans, Britons, and Italians.

I had arrived in Belgium from Germany, a place that should be high on your beer pilgrimage list. Germany is flooded with beer tourists every year during Oktoberfest, an event that typifies Germany’s attraction to the traveling beer lover, with plenty of pilsner, pork, and polkas. Germany is Lagerland, where the cold-fermented, cold-aged quaff is king.

I went to two cities on the northern Rhine River that have stubbornly different beer traditions: Düsseldorf and Cologne. In Düsseldorf, the local breweries make altbier, a dry, slightly roasty dark amber ale. Cologne has its own city beer, kölsch, a light-bodied straw-gold ale that’s crisp and refreshing.

These aren’t quaint local choices, surviving only on the patronage of German beer geeks; they dominate the local markets. It is actually hard to find a pilsner in either place—which is like being unable to find a burger in a U.S. city the size of Detroit.

I had traveled for the true altbier and kölsch experience. In Düsseldorf, I wandered the Altstadt neighborhood, dubbed “the longest bar in the world” in a nod to the 300-odd drinking establishments stuffed into its half-square-kilometer. There is the hausbrauerei (a house brewery—what we would call a brewpub), the Spanish tapas bar, a dive bar favored by crews off the Rhine barges, and fine dining establishments. Every one of them serves one brand or another of altbier, and at most of them, that’s the only beer they have.

In Cologne, which is a 25-minute train ride from Düsseldorf—you arrive at the main train station by the huge cathedral—you find the same situation with kölsch. You can start at Früh am Dom with a hearty breakfast and a couple glasses of kölsch, then stroll down to the Heumarkt plaza and hit a whole string of kölsch houses for a quick glass in each.

And they will be quick: Kölsch is served in small, plain, cylindrical glasses that hold just under seven ounces. Your waiter will keep bringing them for as long as you keep drinking them, making a mark on your coaster each time; when you’re done, you put the coaster on top of the glass and he’ll add up the marks.

Things work the same way in Düsseldorf, except that the glasses hold about two swallows more. I’m usually more of a “try this one, try that one” kind of drinker—but with beer this good, I’m with the locals: Keep ’em coming, and bring me some of that good Rhenish wurst too.

The reason that these beers still hold sway is historical, as Horst Dornbusch describes in his book Altbier. Early Bavarian beer regulations prohibited brewing in the summer, when warmer weather often resulted in soured beer. Brewing in the winter led, naturally, to the evolution of yeast that worked better in colder temperatures. This is what we now call lager yeast.

But brewers in Düsseldorf and Cologne continued to brew in their cooler summers, and the yeast of choice remained the warm-temperature ale variety. Add the determined independence of these two wealthy trading cities—and their traditional rivalry—and you have the reasons that their local brewers didn’t go to lagering. There are other cities in northern Germany that still have indigenous ales: Berlin, with its strikingly tart Berliner weisse and the yeasty, spicy Leipzig gose. But they are not dominant like the beautifully drinkable altbier and kölsch.

I’m happy to say that prospects for the future of these two beers are good. Despite the consolidation that has shaken the German brewing industry, the local markets remain devoted to their city beers. The most serious problem facing the smaller altbier and kölsch makers is one that confronts urban brewers everywhere: There is no room for expansion.

In the Altstadt, I talked to Zum Schlüssel (To the Key) brewmaster Dirk Rouenhoff, who showed me where the brewery had been forced to grow onto the roof and into cellars. “We have nowhere else to go,” he said. The building is classified as historical, “so we cannot change it that much.” A quarter of the brewery’s 15,300-barrel annual production—about the same as that of a healthy American microbrewery—is sold in bottles. Rouenhoff has to send it to an off-site bottling facility because he has no space for a bottling line. It’s a good problem to have, but it’s still a problem.

Each beer type currently represents about 3 percent of the overall German beer market, and almost all of it is sold in or near the two cities. Don’t expect to find any crossover. The folks in Düsseldorf make it very clear that they don’t care for kölsch or Cologne: “You know, kölsch isn’t very good, and their glasses are too small,” I was told more than once in the Altstadt. People in Cologne ignore the existence of altbier and Düsseldorf altogether, offering a lofty indifference when the subject is raised.

When I’m in Cologne, I drink kölsch, and I’m very happy, whether it’s the fresh and grainy glass at the modern Paffen, at the northern end of the Heumarkt, or the malty, more old-style brew at Malzmühle, across the tortuous intersection at the southern end. When I’m in Düsseldorf, I’ll drink Rouenhoff’s fine altbier in its airy home or settle into the more warrenlike environs of Zum Uerige for glass after glass of its classically dry rendering.

It’s a pleasant step out of the pilsner mainstream, in either case, but, really, both city’s glasses are too small for beer this good.