closed book, enigma, secret, whodunit, mystery story, mistery, riddle, whodunnit, mysteriousness, intrigue, more...

clarity, certainty, transparency, openness, obviousness

whodunit, locked room, locked-room mystery, impossible crime, impossible mystery, more...

great, whole, divine, complete, profound, deepest, much, impenetrable, unsolved, paschal, ultimate

unknown thing,   a secret,   unknown location,   detective movies,   hidden secret,   baffling problem,   secret rite,   best kept secret,   unknown object,   unanswered question