Barcelona - a very clean city. Take a Ciy tour (6 hours) included visits to many of Gaudi's architectural sites is a must. Eat tapas at any of the restaurants and visit La Rambla at night. Don't J walk - or you'll be "roadkill"!
Naples - a big dirty city! Go to Pompeii for a tour and admire the ancient planning and building of a 4000 year old city.