We took the excursion to the pyramids and saw the volcano. We went to Colima and had a wonderful authentic lunch, this was an all day tour and worth every penny. Nothing really in Manzanillo, can't fingure out why it is a port.
If you don't take an excursion, there is no where to go or anything to do. I wish Carnival would scrap this as a stop. It cost 8.00 to go to town and back to the ship and I was not comfortable with the local cab drivers.