Lucca's greatest asset is the city itself — the 4-kilometre Renaissance wall that encircles the medieval centre, and the extraordinarily well-preserved fabric of streets, churches, and palaces within. The city has more Romanesque churches per square metre than almost anywhere in Italy, and several medieval towers survive, including the remarkable Torre Guinigi with its rooftop garden. Renting a bicycle and cycling the top of the walls is the single experience most people remember most vividly.