Starting at the Michelwiese, the green beside St. Michaelis, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and set off between port and city. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Hauptkirche St. Michaelis opens proceedings — the 'Michel', whose copper tower has welcomed sailors home for centuries. Riddles ring with Germany's largest tower clock. The Davidwache follows at the edge of the Reeperbahn: the small brick police station that starred in countless films and countless wilder true stories. Trivia stays on its best behaviour. Then the Alter Elbtunnel drops you eighty steps down and 426 metres under the Elbe, a 1911 marvel still tiled like new. Around two hours of harbour air and Hanseatic pride. The leaderboard docks with the final results — moin moin to the winners.