I lived in Belize for a year in Dangriga, but had the opportunity to travel all over the country: Orange Walk, Belize City, Punta Gorda, San Ignacio, San Pedro.
Great place but I recommend you get out of Belize City as fast as possible. Travel was pretty primitive when I was there and I would highly recommend traveling by charter plane as opposed to the buses because the roads were terrible; though I’ve heard they’ve improved the road system a lot since I was there.
San Pedro is a great place to use as a base to get out to the cays which are beautiful. Great place to snorkel. If you really want to relax and do nothing, I recommend the Pelican Resort on South Water Cay. Unbelievable place.
Inland, you may want to try Mountain Pine Ridge in the Cayo district–I think you can do some cave exploration in the area. If you’re interested I can let you know more, but I don’t want to bore you to death. You are going to have a fantastic time.