At the four corners of the Contrary, Visionary, Marvelous, and Phenomenon sims is where you can find the SL7B cake park. Each sim corner has a different "Seven" exhibit and some also have free unique birthday hats.
On Visionary is the Seven Continents Petting Zoo and they have an antlers birthday hat.
Phenomenal has Sojourner's Seven Wonders of the SL World Photo Gallery. I've been to 5 of the 7 displayed, but it's been a while since I visited those sims. I received a landmark to each place when I clicked on their pictures, so I'm for sure going to revisit the ones I've been to before and visit the two I haven't been to yet.
Contrary has a Lucky Seven Games Gallery and they have the jester cupcake party hat. I recommend visiting this place with a group and also pick up some funnel cake!
Marvelous had the biggest crowd when I visited each of the four sims. It has the Lucky Seven Days a Week Nightclub where people can dance and chat. They also have the free birthday cake hat.