First, if you were wondering, you cannot bike back to the ship.
there is a short path from the bike rental, that will take you to the landing strip.
The landing strip will take you to "Serenity Bay".
These are paved, but the landing strip is not smooth since it's supposed to have been there before the island was taken over by Disney.
At serenity bay there is a long packed dirt trail to a very scenic overlook at the end.
Round trip I figure about 3 miles for the entire course.
There are two spots on the trail where water is available.
On the way back, stop at the end of the landing strip and shoot some baskets,
I will be posting a scan of the
Castaway Cay map this weekend.