Are there any tours/ off-site excursions that we should make sure to try while on our trip to CSA in May?

I know some of them take you to the other side of the island and I recall reading something on one post somewhere about a particular excursion not being worth the time it took to get there and back (but would be worth it if you were staying at a resort on that side).

What should we make sure and to while we visit CSA?