Staying on Isla Marina (vs. the larger Rosario island, Isla Grande) was a fantastic choice for the Rosario part of the trip of our Cartagena honeymoon. Coralina Island hotel has everything you want for a romantic getaway - beautiful sunsets, magical nighttime string lights all over the grounds, and A/C in your private accommodations to keep you cool when you need a break from the Colombia sun/heat/humidity. Or of course you can just jump into the glistening water at any dock!
We also went on a snorkeling excursion in the early afternoon; while much of the coral reef in the area has dried up, we did get to see some fish, and simply swimming in the open water under the glistening sun was a delight. Also, Kevin who essentially runs guest services is the best! We are very rusty on speaking/understanding Spanish, so having Kevin around to communicate with (in English) was super helpful, and he made sure we got the best view of the sunset show. :-) Oh and incredible birdwatching is around every corner, and we saw some lizards/iguanas scurrying about. There is so much nature at your fingertips in all of its glory!