Dan,
Caye Caulker is a good laid back location for snorkeling, sea kayaking,deep sea fishing,avoid San Pedro/Ambergris Caye closest thing to a tourist trap in Belize.The beaches are generally poor mostly mangrove,the best ones are around Placencia,Maya Beach,Siene Bight[sand bite sand fleas] and Hopkins.Hopkins is the most laid back,a Garifuna village.For jungle adventure go to CAYO/San Ignacio,Cockscomb basin, or way south near San Antonio Village.
Cayo = Ruins ,Xunantunich is right on the Mopan riverII-III always has water but better high,you can rent duckie ,tubes.or canoes.The ferry man by the ruins will watch your boat for a small tip while you visit the ruins,the best playspot is around the bend an downriver about 1/4 or 1/2 mile,put in at Benque or Succotz take out at Clarrissa Falls.Caracol is the biggest archeological site in BZ,but not well developed and expensive to get to.Go to Tikal in Guatemala if you can,f'ing awesome,daytrips from San Ignacio.
Cayo = caves Actun Tunuchil Muknal highly recommended go with Emilio from Pacz hotel,;Barton Creek cave you canoe thru better value than the Caves Branch where you can raft ,tube ,yak thru 5 of 8 miles underground.
Never been to Che Chem Han but it is supposed to be awesome full of Mayan pottery and you can hike to Vaca Falls on the Macal Gorge.
Cayo =rivers and waterfalls,you can take tours into the Mountain Pine Ridge but is batter to stay at one of the pricey jungle lodges right on a river;5 SISTERS LODGE is on Privassion Creek with sweet rapids right at the lodge[usually too low] you can hike up to a big slide and to Big Rock falls apx. 100 ft with swimming hole.Downstream is awesome but commiting 10 miles w/3-4 [5-] and too big sets of falls to portage[ see my pics in gallery of the 4 mothers] and a run out bottom half of the Macal Gorge 3 - 5+.
Blancaneax lodge; on Privassion expensive owned by Francis Ford Coppola class 5 drop on grounds ,Big Rock falls down stream.
Black Rock lodge at take out for Macal Gorge 2 class 3's on grounds you can hike up to Vaca fall 1 1/2 miles swim /paddle the lagoon to river right and hike up to a series of 3 - 4 drops[4 5 high][
Jeskarper.org index has a video he calls them the wall complex and horseshoe]
Mountain Equestrian Tours is in the Pine ridge recommended.Hidden Valley Inn is pricey but accesses awesome backcountry.
a good deal is Mopan river resort all inclusive tours to Tikal free use of good duckies and tours,i think even booze is included right on the Mopan in Benque Viejo.
Cockscomb has the best system of trails a 2/3 river[harder if you carry way in] and was the 1st jaguar preserve,closer to the beach than cayo.
San Antonio is a village of very friendly Maya way south,Santa Cruz falls squeaky clean 12/15 ftr. into a pool great swimming,cliff diving or if you have a boat you can paddle in the undercut and blast thru the curtain at low water ,real high = death,The UPR. Moho river is maybe the best class 3/3+ on earth up to 60 ledge drops from 5 -20 ft. very plop n drop,high water guantlet of deadly holes,usually run very low by neophytes,a medium level with semi sticky holes but not deadly would be a boofers paradise,might still have water.
also in MTN. Pine Ridge check out Rio ON pools,will make any kayaker drool but usually too low,unfortunately.
You can sea kayak to and camp on a bunch of 'Gilligan's islands'
the Parrots nest on the Mopan in Bullet Tree is supposed to be good, and near El Pilar ruins.
have fun ,pm me with any questions.