Synonyms to castle in the air

Xanadu, airy nothing, autism, bubble, castle in Spain, chimera, daydream, deception, deluded belief, delusion, dereism, dream, dream vision, dreamland, dreamworld, false belief, ignis fatuus, illusion, misbelief, misconception, pipe dream, self-deceit, self-deception, self-delusion, trick, trip, vapor, wrong impression