One of the best dive spot in the world is definitely The Great Blue Hole in Belize.
Just a couple of hours from the cost of Ambergris
Caye, you will find the biggest calcaric hole in the world. Under the 30 meters you can see massive stalactites , they are from the age of the first glaciation.
The dive in the blue hole can reach -42 meters, the temperature of the water is about 28°; it's very important to have a deep diving certification to do it. You will find a lot of big sharks, about 3 meters long, and if you are lucky also some hammer sharks.
During the excursion you will do 3 dives, also one at Half Moon Caye and another at Lighthouse Reef, just perfect underwater gardens.