I believe you need to dive (or at least snorkel) the barrier reef to really appreciate the OUV of this site. That was my first dive in the southern seas (what a way to start, I know), so it does not allow me to compare with any other reef system. I chose to visit on a 3-dive trip to Blue Hole and Half Moon Caye from Caye Caulker. I went with Belize Diving Services. They are highly professional and put a lot of emphasis on security.
The boat ride from Caye Caulker is quite long (2-3 hours) and sea can be rough. The first stop was the Blue Hole. I wasn't experienced and certified enough to do the 40 meters dive to see stalactites (other divers even saw sharks), so I did a 20 meters dive along the hole wall, alone with my dive master. It was still a nice dive. We didn't saw a lot of marine life (fishes here and there, moray eel, spiny lobster), but the colour of the water and the impressive underwater wall steal the show. The dark blue water of the Hole is highly contrasting with the light turquoise of the shallow waters around.
The second stop was Half Moon Caye. This dive was the most amazing one of the day. It goes to a shallower depth but this site is much richer in marine life, including big stuff. We saw Caribbean reef sharks, spotted eagle-rays, a loggerhead sea turtle, barracudas, angelfishes, parrotfishes, triggerfishes and so much more. Half Moon Caye is also the island where we stopped for lunch. It's still unclear to me whether the islands are part of the WHS or if only the sea is, but I do hope the islands are included as well. The island is famous for being one of the few nesting sites of the red-footed booby in the Caribbean. We took a walk to see the nesting site after we had lunch. We can climb a tower to get really close to the nesting boobies and frigatebirds. Other wildlife of the island include iguanas and hermit crabs everywhere. Two endemic lizards also live on the island.
The last dive of the day was Long Caye Aquarium. This site is quite similar to Half Moon Caye. The corals and sponges are abundant and seems healthy. We again saw sharks and eagle-rays as well as a lot of fishes. Dolphins were swimming near to the boat when we got out of the water. It was an incredible day and I will remember my first dives in coral seas for long.