puzzle box

Short definition from Wiktionary

Noun

1. 1
   A box that cannot be opened by the usual obvious means, and therefore challenges a person to find the correct way to open it.
2. 2
   A similar device or cage that can be opened by means of levers, latches, etc., used to test the learning behaviour of animals.
3. 3
   Something that is puzzling; an enigma; (narratology, also attributive) a complex story that is gradually revealed, often driven by a central myth.
4. 4
   A box containing a jigsaw puzzle.
5. 5
   Alternative form of puzzle box