Düsseldorf's Altstadt houses the highest density of breweries per square kilometre anywhere in Europe. Within a five-hundred-metre corridor along the Rhine, six independent brewhouses still ferment Altbier using open copper vessels and wooden casks unchanged since the 1850s. The word "Alt" means old—not in age but in method, distinguishing top-fermented copper ale from the bottom-fermented lagers that swept Germany in the nineteenth century. When Bavarian brewers adopted cold fermentation and pale malts, Düsseldorf's guilds refused. They continued mashing dark Munich malt and fermenting warm, preserving a brewing lineage older than the unified German state. Today that refusal defines the Altstadt's identity. The quarter's breweries—Uerige, Füchschen, Schumacher, Schlüssel—function as neighbourhood anchors rather than tourist venues. Each operates a brewery tap attached to its fermentation hall, serving Altbier within hours of casking. The beer arrives in cylindrical 200-millilitre glasses carried on wooden trays by servers called Köbes, who wear blue aprons and replace empty glasses without being asked. This system, called Kranz service, emerged in the 1920s when breweries needed rapid turnover during Weimar inflation. Visitors accustomed to ordering individual drinks often find their table accumulating glasses faster than expected. The Köbes mark consumption with pencil tallies on cardboard coasters, settling accounts only when a guest places a coaster atop the final glass. Düsseldorf beer tasting tours navigate this ecosystem by pairing brewery visits with historical context. Guides explain malt roasting schedules, yeast propagation methods, and the 1873 guild ordinance that restricted Altbier production to family-owned houses within city limits. Most walking routes begin at Bolkerstrasse, the Altstadt's central artery, then move through cobbled alleys connecting Ratinger Strasse, Kurze Strasse, and the Rhine promenade. Each brewhouse occupies a repurposed medieval merchant hall or Hanseatic warehouse; stone vaults and timber joists remain visible beneath electric lighting installed decades after the buildings went up. The Altbier itself pours mahogany with minimal head, tasting of biscuit malt, subtle hops, and a dry finish absent in sweeter German styles. Alcohol content holds steady near five percent, low enough for the three- to four-beer progression typical of an evening walk. Seasonal releases appear in winter—Sticke, a stronger variant with intensified hop bitterness, brewed only in January and October. Guides on dusseldorf beer tasting tours time visits to coincide with cask tapping or explain barrel cooperage in brewery cellars still lined with nineteenth-century oak. The experience privileges process over spectacle, immersion over entertainment.