If you visit Tarragona, you can't leave without having an al-fresco vermouth on one of the terraces in the plaza. The local custom is to go and have a drink around noon. I’d suggest Casa del Vermut in the Plaza del Rey. You can sit out on the square with a cool vermouth in hand and have a lovely time just watching the world pass by. They even gave us croquettes as a personal touch and they were delicious!