At the Cape Canavaral terminal, you board on deck 3. Once the ship leaves port, the opening you entered through no longer look like regular doors.
As mentioned, Castaway Cay (as well as most ports) you board on deck 1.
I believe someone mentioned on the California cruise, they either embarked or disembarked on deck 4. They had CM's assisting passengers on the stairs with their carry on luggage. I don't know if this was a single occurance, or all the time in CA.
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