For the new people here on the board.
Okay, I have never been to Atlantis, but as I have really researched this as a possibility for our cruise, here goes...
As mentioned, The Atlantis does not offer a day-use. Anyone can stop by, but will have restricted access. The casino is open to all. 'The Dig' (aquariums) run around $25.00 to go thru.
( check out Atlantis.com )
Disney does offer two excursions to Atlantis.
1. Discover Atlantis - which includes The Dig $33.00 for ages 10 and up, $23.00 ages 3-9
2. Atlantis Beach Day - which also includes their beach and lunch at a lunch/snack bar $60.00 for ages 10 and up, $45.00 ages 3-9
Otherwise, the pools and slides and beaches are only open to guests of the Atlantis or the Comfort across the street. Limit is 4 guests per room. Guest are given a wristband.
So. Pricewise for a family of 4, the Atlantis Beach Day would run $210.00. For less money, it does make sense to get a room at the Comfort, have full access to Atlantis, and use the room to shower and change if you want. Also, you can return to the ship as late as you like.
The shore excursions take a water-taxi over to Paradise Island. If you go on your own, I think it is supposed to be easier and faster to take a taxi from the dock right to The Atlantis.
Hope this helps. And if I have anything wrong here, you guys correct me!