O’Brien’s Cay “aka” The Aquarium. This dive site is appropriately named, as it’s home to a thriving diversity of aquatic life which you can view in its natural habitat. O’Brien’s Cay is one of the lesser-known islets within the marine park and is home to a natural wonder known as the Aquarium. Snorkeling in this dive site really does feel like you’re inside a tropical fish tank, with kaleidoscopic shoals of fish floating past everywhere you look. Many of the Sargent Major fish will even swim right up to you! What makes this spot so unique is the wall dive where you can see schools of yellowtail snappers, parrotfish, grouper, as well as coral, purple sea fans, and sponges. Many nature lovers say this is their favorite stop.