This enormous and enormously remarkable structure is the star of Cologne, the city celebrity with top billing. Considering how much time passed during the construction of this gigantic edifice, the largest cathedral in Germany and all of northern Europe, it’s a wonder that the Gothic facade is so stylistically coherent. More than 600 years elapsed from the laying of the cornerstone in 1248 to the placement of the last finial on the south tower in 1880. Upon completion, Cologne cathedral was the tallest building in the world, its twin filigreed spires rising to a height of 157m (515 ft.). Overwhelming is the simplest way to describe it—as you’ll discover when you step inside.

The cathedral was built to enshrine holy relics—in this case, relics of the Three Kings or Magi—which had been stolen from a church in Milan by Emperor Frederick Barbarossa. These relics, which drew pilgrims to Cologne throughout the Middle Ages, are still housed in the Dreikönigschrein (Shrine of the Three Magi), a glass case at the end of the cathedral choir. The giant reliquary is a masterpiece of goldsmith work dating from the end of the 12th century. The choir, which can be visited only on guided tours, was consecrated in 1322 and contains original, richly carved oak stalls, screen paintings, and a series of statues made in the cathedral workshop between 1270 and 1290. The famous Three Kings windows in the clerestory were installed in the early 14th century. In addition to some magnificent Renaissance-era stained-glass windows in the north aisle, and German artist Gerhard Richter’s darkly shimmering stained-glass windows in the south transept, installed in 2007, the cathedral has only two other conspicuous treasures. The Gero Cross, hanging in a chapel on the north side of the choir, is a rare monumental sculpture carved in Cologne in the late 10th century and reputedly the oldest large-scale crucifix in the Western world. On the south side of the choir is Stephan Lochner’s altarpiece, “Adoration of the Magi” (c.1445). The painting is a masterpiece of the Cologne school—Italian in format, Flemish in the precision of its execution.

The cathedral’s Schatzkammer (Treasury) is rather disappointing, and you aren’t missing much if you skip it. If, on the other hand, you’re in reasonably good shape, climb the 509 stairs of the 14th-century south tower (entry through the Portal of St. Peter) for an inspiring view of the city and the Rhine. The cathedral is now a UNESCO World Heritage Site.