CityVille: Watch dolphins do tricks in your new Aquarium
From there, you'll need to staff your Aquarium with 10 friends in total, but two might have been filled in for you by Samantha. You'll be able to hire friends by clicking on the "Hire Friends" button and sending individual gift requests to those friends that you think would be most likely to help you.
The Aquarium is an open-air arena, and you'll apparently be able to watch dolphins perform through a hoop above the water once the building is completed, so if that doesn't give you enough reason to build one, I don't know what else will.
Have you built your Aquarium in CityVille yet? What do you think of this new Community Building? Let us know in the comments.