Curaçao Sea Aquarium focuses on marine life from the waters around the island. Its open-water system continually draws seawater into the tanks, and the visit combines aquarium exhibits with scheduled feeding presentations and close views of turtles, sharks, rays, and reef fish.
It is beside Mambo Beach, so the two are easy to combine. Allow a few hours and check the day's presentation times before setting out; much of the value lies in the guided sessions rather than simply walking past the tanks.