Starting at the Portal del Roser on Via de l'Imperi Romà, a gateway in the old Roman walls, you'll open the Explorial app, enter the 6-digit game code that you received by text and Viator chat message, and step into the old town. The tour is fully self-guided — no guide, no fixed start time, just your group and the city. At the Plaça dels Sedassos, riddles point you toward the square's famous trompe-l'oeil mural — a painted balcony scene locals treat as a neighbour. The Catedral de Tarragona crowns the highest point of the city, layering Romanesque and Gothic over a Roman temple site; its cloister and carvings hold answers you'll have to hunt for. Then the route rolls downhill to the Balcón del Mediterráneo, the iron-railed lookout above the Roman amphitheatre where touching the railing — tocar ferro — is said to bring luck. About 2 hours in the Mediterranean sun, vermut stops optional. By the end, Tarraco will feel less like a ruin and more like a living city.