I went to Varadero last year for a wedding, and the couple chose to do the catamaran tour to Cayo Blanco. About half the group went and we had a fabulous time!! It was for sure one of the highlights of our trip.
You get picked up around 9ish and it is a really fun day...they serve drinks on the catamaran and at the island Cayo Blanco (that made the day even more fun lol) and there is a full buffet as well. They offer a lobster tail on the catamaran for 10 pesos which was THE BEST I have ever had....totally worth it and my fiance and I still talk about it!
The guide for the day was so full of energy and on the way home we had a dance party on the boat. When we go down next May this is 100% on our list to do with our guests.