The aquarium and open-sea oceanarium on Isla Rosario is a regular stop on the standard day-tour circuit from Cartagena. It houses Caribbean marine species including sharks, rays, sea turtles, and tropical fish, and the oceanarium section allows snorkellers to swim in an enclosed open-water area alongside some of them.
It is a reasonable attraction for families with children, and gives non-swimmers a way to see the marine life up close. For experienced snorkellers or divers, the wild reef sites in the park are considerably more interesting, but the aquarium provides context for what you will find out there.
Stop times on day tours tend to be short — typically 45 minutes to an hour. If you want longer, it is possible to visit independently by hiring a private boat from Cartagena.