In Grand Cayman the best excursion is snorkeling with the Sting Rays. YOu can sign up for a ship excursion or find an independent tour operator there, but either way, its a great way to spend the day in Grand Cayman.
We went up to the beach at the Holiday Inn. The cab ride is only about $4 per person and the beach is free. If you want to rent a chair, for $10, you can rent a chair and get a coupon for a soda/water. Also, there are facilities right there and an outside grill/restaurant.
Isecond Peas post, go to the beach it is lovely!!! The turtle "farm" is just that , yuck, a bunch of turltes in a VAT. And of course a gift shop. Don't bother.
Hell is nothing but a field of lava formations, you statnd on a platform and lokk at them. Ohh wow, now what, oh yes the gift shop, and a postcard that you can send postmarked "Hell" . Whoopee!
Now the beach is truly beautiful, and you can easily rent a chair, but a drink and relax!!!!
The tour with the stingrays things DOES sound great, if you like that sort of thing, and it has had consistantly good reviews, so if you think you'd enjoy it then book it.
We booked a snorkeling tour outside of the ship with a company called Soto's Cruises. It was $19 to go out for 3 hours, and they to you to 3 spots, including Stingray City. The guide was awesome; he chased a morray eel out of a hole and showed it to us, he pointed out a family of nurse sharks, and he taught us how to pick up the stingrays. It was one of the best vacation experiences I've ever had, and GREAT photo opps if you purchase a disposable underwater camera.