Just returned from cruise and did an excursion through our ship to Barbados that was a rainforest hike and cave tour. I would highly recommend it for those who are fit. The rainforest tour was interesting and about 3/4 mile? The cave tour was not Harrison's cave (where you go through on an electric trolley). It is on foot and at times, hands and knees as some portions of the caves were quite low / tight. There was also significant water in portions of the cave, so expect to be wading. Overall, one of the better excursions we've ever done.
We did go to St. Lucia, but did not do a jungle tour there.