There is no decent scuba diving that I know of in the immediate vicinity of Cartagena. There apparently are several dive sites well east of the city. I visited two, both on the same day. They were ok, not spectacular, but enjoyable enough. Standard Caribbean diving, median quality, not a diving destination, really. I was lucky to hit a patch of good weather. I went primarily to visit Cartegena, which is spectacular in so many ways. It's the centuries old city that plays a central role in many of the fantastic and magical works of Garcia-Marquez. This was not my first time there, and it will not, I hope, be my last.