Seadome the Neptune level? I assume you know where the circuis is, once you get big enough to roll up cars (around that size, not really sure, but it wasn't there when I first looked, after getting past the 3m barrier), check the pier for a barge/boat with a present on it. If taht is the only one you are going after, just keep checking after every size increase in that area. Start from the circuis tent and go down to the water.
Oh THAT Circus. Thanks, that helped a ton.. I was going to the 'amusement park' section, with the roller coasters, etc. It's actually the circus right near the water outside of the opening towns.