Synonyms to castle building

Walter Mitty, absence of mind, absentmindedness, absorption, abstractedness, abstraction, bemusement, brown study, daydream, daydreamer, daydreaming, depth of thought, dream, dreamery, dreamfulness, dreaminess, dreaming, dreamlikeness, engrossment, fantasy, fantasying, fit of abstraction, mooning, moonraking, muse, musefulness, musing, muted ecstasy, pensiveness, pipe dream, pipe-dreaming, preoccupation, reverie, stargazing, study, trance, woolgathering