The Two Oceans Aquarium sits at the V&A Waterfront and is one of the best-presented aquariums in the southern hemisphere, with its exhibits organised around the two oceans whose currents meet at the Cape of Good Hope. There are kelp forests, an open-ocean tank with rays and sharks, a tide pool, and an Indian Ocean tropical gallery.
The aquarium runs a strong conservation programme, particularly around sea turtle rescue and rehabilitation, and you'll often see recovering turtles in the back tanks. Two to three hours is enough for a thorough visit, with cheaper entry after 14:00. Good for children but not aimed exclusively at them.