There are three airdocks on towers around the battlements, and a large platform level with the lowest wall that the flying castles can extend drawbridges onto.
A large stone platform is levitated up and down a hole trough the center of the largest castle like an elevator, providing access to the ground level city. Secret spiral staircases wind up the interior of some of the pillars (which prevent the castle from drifting, rather than supporting it's weight.)