You can certainly see why no one could conquer the old walled city of Lucca.
It is a great site to visit and spend time walking along the top of the wall, or bike (they rent them there). Like all of Italy this site is second to none. Don't just stick to the wall, walk in the old city and get lost in it. You will find your way out, don't worry.
Hungry? go to Ristorante Bucadisant, one the best of the best 5 star restaurant I have ever experienced.