We did this last October on Sovereign. We thought is was not worth the price.that RCCL charges. Walk down to the ferry and take the ferry on your own over to Atlantis. Much cheaper then the RCCL prices. I have learned through experience to book excursions on your own whenever possible. Save a bundle. You can learn who to book through by reading the posted messages. There are many reputable excursion companies on all of the Islands. When we went with RCCL we did not get lunch or a beach chair. Just rum punch on the ferry over to Atlantis. Very dissapointed with this particular excursion with RCCL.
There are 2 Atlantis trips offered through RCI. One comes WITH a lunch, beach chair, tour, and ferry ride. The other does NOT come with beach,lunch. The $65.00 tour DOES come with lunch, beach and beach chair. The brochure you get with your final doc's explains what the tours cover and how much they cost. And yes , you can take a cab over and get dropped off right in front instead of walking 10 min. from the ferry. They charge $25.00 adult and $19.00 child to tour the Digs at Atlantis(this is the hotels price to tour) which is what people usually want to see. To get to the beach you can walk around the side of the hotel (not through) and use the beach for free, just no beach chair.
Hope this helps :wave