At Belize, we booked with Reggie Trapp for his Cave Tubing adventure@ $65pp. It is not that strenuous, but a lot of fun. It is a great way to do something different, learn and see a beautiful country and meet other cruisers. Check out www.regtours.net
. The advantage of a ship's tour is that you will get off on a tender first and be back on time. Reggie has never missed the boat in over 5 yeas of being a licensed tour guide. There are many private tour guides, so keep checking the ports forums on this site as well as other similar web pages for great reviews and first hand experience.