Starting at 44 Bis Rue Mignet, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and slip into the old town's honey-coloured lanes. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Place des Prêcheurs opens proceedings, its market-square bustle hiding centuries of sermons, trials and spectacles that riddles are happy to revisit. The Place d'Albertas follows like a stage set — a perfect baroque square built by a marquis so his view would match his ambitions. The photo task takes care of itself. Then the Cathédrale Saint-Sauveur closes the route, a building that grew ring by ring from Roman baptistery to Gothic nave. Around two hours beneath the plane trees, fountain stops encouraged. The leaderboard pours out the results — chilled, like everything in Aix.