Starting at Büchel 29-31 in the old town, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and follow the lanes toward the cathedral. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. The Aachener Dom rises first — Charlemagne's octagonal chapel, over 1,200 years old and Germany's first UNESCO site. Riddles circle the emperor's throne and a legendary deal with the devil. The Elisenbrunnen follows, the classical colonnade where sulphur springs steam as they did for the Romans. Trivia holds its nose and carries on. Then the Rathaus commands the market square, built on imperial palace walls and hung with the crowns of thirty coronation feasts. Around two hours through the city of kings, Printen gingerbread at arm's reach. The leaderboard performs the final coronation.