Might I recommend nests or a hive? If you really want to bend their brains, how about something Escheresqu? You've likely seen the optical illusion of stairs that converge (drawn by MC Escher). Think crazy things like that. Then go back to using a castle.

Might I recommend nests or a hive? If you really want to bend their brains, how about something Escheresque? You've likely seen the optical illusion of stairs that converge (drawn by MC Escher). Think crazy things like that. Then go back to using a castle.