Lucca's Renaissance walls are 4.2 kilometres long, 12 metres high, and — most importantly — still intact. Built between the 16th and 17th centuries when the city feared absorption by the Florentine Medici, they were designed according to the most advanced military architecture of the era, with earthen ramparts so thick that cannon fire could not breach them. The threat from Florence never materialised, but the walls survived, and the city planted the broad promenade of elm trees along the top that you walk today.
The rampart walk is the defining experience of any visit to Lucca — broad enough for cyclists and pedestrians to share comfortably, shaded by elms, with views down into the gardens of the palazzi inside the walls on one side and the flat Tuscan plain on the other. Cycling the full circuit takes about 40 minutes; walking it takes 90. Bicycle rental is available at several points along the walls.