Starting at 3 Place des Orphelins, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and head across the Grande Île. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Quartier de la Petite France unfolds first — half-timbered tanners' houses leaning over green canals, every corner a riddle-worthy view. On Place de la Cathédrale, the pink sandstone cathedral fills the sky; for over two centuries it was the tallest building in the world. Trivia covers the astronomical clock and its noon parade of apostles. Then the Église Saint-Thomas offers a quieter finale, with a marshal's spectacular mausoleum and an organ Mozart once played. Around two hours between France and Germany, culturally speaking. Tarte flambée seals the final standings.