Starting at Bahnhofstrasse 3, near Thun's station, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and make for the old town. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. On the Rathausplatz, the riddles start among arcades and flower-decked facades, with the castle looming photogenically above every answer. Then it's up the covered stairs to Schloss Thun, the 12th-century Zähringen keep whose four corner towers have become the town's signature — the knight's hall and the views both reward the climb. The Stadtkirche completes the skyline: its rare octagonal tower has watched over Thun since the Middle Ages, and its terrace looks out across the Aare to the Alps. Around 2 hours between castle, church, and riverbanks, with Aare-side breaks encouraged. By the end, Thun will feel like the perfect first chapter of the Bernese Oberland.