There are two ramblas in Tarragona. Rambla Vella that sets the border to the old town is fairly dull. Instead, it is Rambla Nova a few more blocks from the old town that is the main drag. It starts at Balcó del Mediterrani where there are plenty of cafés and between the car lanes there is a wide area perfect for a stroll. Right now, it's a quiet Sunday afternoon.