I strongly recommend getting a room at Comfort Suites, which you will never see, then spending the day at Atlantis. Much, much cheaper than
DCL, and very easy to get there and back by cab:
Typically, the least expensive way to visit Atlantis is to book a room that you will never use at the Comfort Suites, across the street from Atlantis. They have full use of the waterparks and charging at Atlantis, and you can often get a room there for around $200 for a family of four.
For example, someone sailing a four night Bahamas cruise on the Dream that departs Port Canaveral 8/3/14 and visits Nassau on 8/4/14 would book a room at TheComfortSuites for 8/4/14. You would tell theComfortSuites that you will arrive on 8/4/14 and depart 8/5/14. Of course, you will actually depart in the afternoon of 8/4/14, but they don't care.
On 8/4/14, wake up, eat breakfast, and take a cab to theComfortSuites. Do NOT take a water taxi. While slightly fun, they wait for the ship to fill, so you get to waste 20 or 30 minutes, all the while breathing in diesel fumes, while they fill the boat. Take a taxi to theComfortSuites.
Check in at Comfort Suites. Your room is not ready, but it does not matter, as you will never use it. Get your wrist bands, and then head over toAtlantis, easy walking distance. (I can't remember if you get your bands at Comfort Suites or take a paper from Comfort Suites to Atlantis and get your bands there, but it doesn't matter, the Comfort Suites receptionist will guide you through it.)
Enjoy Atlantis. Tour the grounds, use all the slides, charge a bunch of food and drink back to your account at The Comfort Suites using your wristband.
When you are sunburnt and tired, grab a cab and go back to the ship. As the ship sails away, look at your family and smile about all the great times you had today. Your food and drink will be added to your account atComfortSuites, which will automatically close out tomorrow morning. You won't be there to get the paper receipt, but that doesn't matter.
We have done this twice. It is a great way to enjoy Atlantis and save a few hundred dollars versus a DCL excursion. Have a great time!