Porto is the second largest city in Portugal after Lisbon. It (1) is one of the major urban areas of the Iberian Peninsula. Located along the Douro river estuary in Northern Portugal, Porto is one of the oldest European centres. (2) In 1996, UNESCO recognised its historic centre as a World Heritage Site. Among the architectural highlights of the city, Porto Cathedral is (3) the oldest surviving structure. It attracts millions (4) of tourists every year.