puzzle box
Noun
Meaning
A box that cannot be opened by the usual obvious means, and therefore challenges a person to find the correct way to open it.
A cage that can be opened from the inside by means of levers, latches, etc., used to test the learning behaviour of animals.
Source: en.wiktionary.orgExamples
In this award-winning horror short, an elderly man purchases a mysterious old puzzle box with the intent of solving its hidden meaning.
The man drives his old car to his old house, where he puts on an old record on his old player, and begins to work on the puzzle box.
The puzzle box is one of the best objects of its kind in any film and is a key part of the story.