Starting at Place de la Planta 1, the city's great gathering square, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and set off into the old town. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. At the Cathédrale Notre-Dame du Glarier, riddles gather beneath a Romanesque belfry that has survived fires, sieges, and centuries of Valais politics. La Grenette adds a mercantile chapter: the elegant old grain exchange where farmers once haggled under the arcades, now one of Sion's best-loved buildings. On the Place du Midi, the trail threads between café terraces and shopfronts where the medieval city gives way to the modern one — with the castle hills of Valère and Tourbillon photobombing every view. Around 2 hours beneath the vineyards, with Fendant wine stops at your discretion. By the end, Sion will feel like Switzerland's best-kept secret.