Look down at the Kö from a low approach and the boulevard reveals its strangest feature: a 31-meter-wide canal running straight up the center, lined on both sides by chestnut trees and crossed by a pair of iron bridges. The whole esplanade stretches roughly 80 meters across and a kilometer long, fed by water diverted from the Düssel, the little river that gives Düsseldorf its name. It is not a Venetian afterthought. The canal is older than almost everything around it, completed between 1802 and 1804 when court architect Caspar Anton Huschberger, landscape architect Maximilian Friedrich Weyhe, and hydraulic engineer Wilhelm Gottlieb Bauer turned the line of a demolished fortification into a Classical promenade. The chestnut trees were Weyhe's idea, and for a while they gave the street its first name.

After 1946, North Rhine-Westphalia found itself the most economically powerful state in a country starting from rubble, and Düsseldorf was its capital. The German fashion industry consolidated here, drawn by money and proximity to the Rhine industrial heartland. In 1949, an open-air fashion show on the Kö launched the first Igedo Fashion Fair, which grew into one of the largest in the world. Since 1981, the city has hosted the biannual Düsseldorf Fashion Shows under the name Collection Premieres Düsseldorf, with most runways at the Messe but showrooms scattered through the streets. The Kö's eastern side became a wall of flagship stores. Its western side stayed quieter, given over to banks, hotels, and offices that watch the spending happen across the water.

In 1984, the singer Herbert Gronemeyer released his hit Bochum, an affectionate anthem to a grittier Ruhr city up the road. The song name-drops Düsseldorf's Königsallee only to dismiss it: in Bochum, Gronemeyer sings, what counts is the heart, while in Düsseldorf what counts is the money. Bochum has its own Königsallee, an unimpressive thoroughfare that exists mostly so the joke lands. The Kö took the teasing in stride. By any sober measure it is one of the busiest upscale shopping streets in Germany, and recent surveys have placed it among the most expensive luxury retail addresses in the country, second nationally behind a handful in Munich.

Walk north along the canal and the Kö opens onto the Hofgarten, the city's main park, where the boulevard pushes out onto a small lake peninsula called Landskrone. That northeastern corner used to be a tangle of postwar planning compromises until Daniel Libeskind got hold of it. The architect of Berlin's Jewish Museum designed the Kö-Bogen, a 40,000-square-meter office and retail complex of curved glass and angled cuts, with the first sections opening in autumn 2013. It is the kind of building that argues with its surroundings on purpose, and it gives the historic boulevard a deliberate new ending — a hinge between the old chestnut canal and the modern city behind it.

From the Hofgarten to Carl-Theodor-Strasse at the southern end, the Kö covers about a kilometer. The Altstadt sits one block west, with its hundreds of bars in the so-called longest bar in the world. Schadowstrasse, which has higher overall sales than the Kö, runs off to the east. The luxury shops cluster on the east side: Hermes, Louis Vuitton, Chanel, Gucci, Cartier, and the rest of the roll call, often inside block-internal arcades that thread through to side streets. The Breidenbacher Hof, the InterContinental, and the Steigenberger Parkhotel handle the guests. Cafes line both banks of the canal, and on a warm afternoon the chestnut shade and the slow water make even the most aggressive shopping street feel briefly like a park.