Trevor and I recently stayed at the Copamarina Resort in the south. My Dad and step-mom took care of our kids for three days. Yay! For $10 a person, the resort will ferry you over to the little Guilligan’s Island. Not a three hour tour, haha. A 7 minute ride.
The main attraction is the mangroves and all the fish and coral that surround them. Just wanting to check it out for future visits, we didn’t have snorkeling gear. But we did enjoy watching the schools of fish in the very clear, and strong currented water. 
There are no facilities here except baños. Plenty of shade, no beaches to speak of, so get in the water and swim around!
Mangrove trees were interesting. Overall, I don’t think I’ll bring our kids here until they are. Enter swimmers and can do a bit of snorkeling. But I’d love to return with Trevor and full face snorkel masks!
Some nice people let us try their full face snorkel mask. Sold! Put it on my birthday list…
So glad you guys got to check out Guilligans Island! We loved taking our kids there (they are older) and loved to snorkel a big circle all the way around the mangroves to the other side back around. The current pretty much just takes you along.