Well, if we'd been there before we probably wouldn't have a plan....but hey, I am a planner-type gal so this is what I do.
I just want to have a map in advance & find out where the adult beach is, how long the walk is, where the bbq is in relation to the adult area and where we can rent bikes. Yep we don't even "wing it" for beach days!
http://www.mickeyxtreme.com/castaway_cay_map.htm
This may be same map Lauren posted. Well, yeah, same map; I mean same link.
If you are the first off the ship, it's sort of like seeing a small town come alive in the morning; people heading out to duty stations, getting things set up for the cruisers. The concessionaires arrive from Abaco Cay via boat to guide us out on wave runners, fishing boats, catamarans, parasailing.
When you get off the ship, you can exit from fore and aft, right onto the pier/concrete "Arrival Plaza" They'll hand you one (or two) towels to use at the beach. If it's early, the Post Office may not be open yet. Eventually, the photographs are set up to catch you posed in front of the Magic, the Flying Dutchman and several other vantage points. If you are doing a fishing boat (or other activity where they drive you in the boat), it's the first stop on the left.
But still, you are walking. It's not long; 5 minutes of less and you are at the first Tram Stop (Kargo Handling). If you don't ride, it's only about 5 more minutes to the "downtown" of Castaway Cay. Gift shops, bath rooms (with outdoor showers), towel drop-off, First Aid; bars, Cookie's BBQ for family lunches. For bike rental, just keep going through "downtown" - they have good signage on the boat and island.
If you are going to the adult beach, you'll probably catch the tram at the Palm Central Station Tram Stop; otherwise, it's the longest walk on the island. The tram will drive you down the old runway to Serenity Bay.
And there, it's pretty concentrated. To your left is the lunch area, straight through is the beach. You pass a bar and bathrooms about 30 feet in; the beach runs out to your right with chairs, chaises and hammocks.
The water is about chest-high on me (I'm 5'9") for farther out than I'd consider going. There are coral or rocks on the bottom, so I wear water shoes. It is usually very clear, fairly calm (unless the wind picks up) water. If you wore swim goggles, you could just put your face in the water and see the same stuff as with a paid snorkel set. I've never seen many fish there.
Lunch is offered for a limited time. You will receive info about our CC day the night before along with the daily Navigator.
I've heard that bike rental is nearly always available; just wait until you get there (it will be a room charge, anyway).
Happy planning,
Lynne
It is really this coming week on Thursday but I couldn't get this cruise started any earlier. 
It's hard to believe that people as young as we are have a DS that OLD! 
Sending hugs and prayers 
That's the one day of this cruise that is free - everything else has 
Seriously, it looks like you had a BEAUTIFUL time.
Pixie Dust for your Mom.
