When you have done the main attractions of Pisa, there is still one little gem left: Marina di Pisa, the harbor of Pisa at the Mediterranean sea. It hosts a beach, not with sand, but with little marble pebbles. The pebbles are smooth, and will not harm your feet, but since they are slightly unstable near the water, sea water compatible footwear is recommended for walking along the beach and getting in or out of the water.