Starting at Rotteckring 5, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and follow the Bächle — the little water channels — into the old town. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Münster anchors everything: its filigree spire, called the most beautiful in Christendom, survived the 1944 bombing almost alone. Riddles climb through gargoyles and market noise. At the Neues Rathaus, trivia rings with the carillon over Rathausplatz, where the university town's civic pride blooms in window boxes. Then Konviktstraße seduces at the end — wisteria, cobbles and craft shops in the old town's prettiest lane. Around two hours in Germany's sunniest city, Black Forest air included. The leaderboard decides who wins; the Bächle decide who gets married.