Well, there is so much to do that it would be impossible to do all of it in a short trip!
In addition to the diving, here are other things to do:
Mayan Ruins:
Lamanai is one of the largest, and the New River jungle river tour on the way to Lamanai is supposed to be awesome
also La Milpa
Cave Tubing: at Caves Branch or others
Caving: at Caves Branch or other caves
Jungle Tours:
Rio Bravo Conservation Area
Cocksbomb Basin Wildlife Sanctuary (Jaguar Reserve)
Community Baboon Sanctuary
Bacalar Chico
Crooked Tree Wildlife Sanctuary
Night jungle tours/safaris
Belize Zoo
Manatee watching: near Swallow Caye or other areas
Waterfalls
Sailboarding, Sailing
Fishing
Those are just SOME of the interesting things to do in Belize.
I haven't been yet, but I'm planning for my trip in January.
So much I want to see, so little time... :loopy:
Some websites:
http://www.travelbelize.org/
http://www.belizenet.com/
http://www.belizeit.com/index.htm