That was Caves Branch you saw on TV. It is a very cool trip on the mainland out in Cayo. You tube in a mile or so against a light current, have lunch on a sandbar in a very dark cave, and then float back out. You'll see bats and other cool critters in there. Mayan artifacts are everywhere. For a traveler like you I'd suggest Monkey Bay as well. Real wildlife for the hardy. No tourist trappings. Not soft but very close to nature. The Sibun is a great place to cool off.