Starting at the Brauerei Zum Schiffchen on Hafenstraße — Düsseldorf's oldest tavern — you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and head into the Altstadt. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Kuhna-Mauer opens the hunt with fragments of the city's fortified past, hiding in plain sight among the lanes. Riddles do the excavating. The Basilika St. Lambertus rises next, its famously twisted spire the subject of legends involving the devil, bad timber and one embarrassed carpenter. Trivia sorts fact from folklore. Then the Tritonenbrunnen splashes at the Rhine promenade's edge, sea gods wrestling as joggers drift past. Around two hours through the 'longest bar in the world' — 300 taverns in one square kilometre. The leaderboard names its champion; an Altbier toast follows naturally.