I took the water taxi and walked down the hill, in my opinion t wasn't a long walk (approx. 1/4 mile). You can also take a taxi that will take you to the front door. Once you walk through the Casino you will see a restaurant when you reach the restaurant you will see that there is an aquarium covering the wall of the restaurant and it is probably 10 feet tall. You can walk right up to the side of the aquarium and look a shark in the eye.
No problem getting there, just take a taxi. They are everywhere. It only takes a few minues. Also, Atlantis gave us a deal. We had six people, but they let us use a room for the day (including all faciliies and amenities) for $200 until 6:00 pm. We were guests of the hotel so we could go down water slides, use pool, visit aquarian, etc. We did this ourselves, not through the cruise ship and the $200 was a lot less than we would have to pay for a shore excursion for 6 people. We had a fabulous time and would do it again in a heartbeat. At 6:00 we all showered in our room and toured inside of hotel. There are fabulous shops and restaurants. We also played on the largest minature golf course I've ever seen.