This puzzle has been made in smaller sizes, but when Royal Magic (Fun, Inc) came out with a puzzle box big enough to hold a full poker-sized deck... well, this is something that magicians may want to take notice of. More of a puzzle than a magic trick, but a very puzzling puzzle, to say the least.
This clear plastic box does not seem to have any way to get it open. And yet there is a hundred dollar bill (for example) inside. Or you can borrow an attractive stranger's hotel card key, and after placing it under the bar table briefly, you bring out the puzzle box with her card key sealed inside. Tell her you will show her how to get it out, but only once you are outside her hotel room door... (Okay, maybe that particular usage of the puzzle box is not for everyone.)
Because the box can hold a deck of cards, most dealers showed this item (when it was readily available, which it is no longer...) with a deck inside the box. My picture also shows it this way. but I will tell you something other dealers never did: when a heavy item like a deck of cards is in the box, it is very possible to discover the secret opening because the weight of the cards helps open the box. So it is not really suitable if your plan is to hand a spectator the box and ask them to get the cards out. But you may wish to use it like I sometimes do. I keep a deck in the box on my mantle at home, and when the conversation turns to magic, I show the deck inside the sealed box. Have someone take out a twenty dollar bill and fold it into quarters. As they do this, pop open the box and hand the deck to someone. Take the twenty and place it into the box and close it. All this happens before anyone knows what is happening. Set the box aside, and show a few tricks with the deck. After the card magic, mention that the owner of the twenty dollars can have it back... all they have to do is open the box. (Because the box opened so easily with the deck inside, the mystery is heightened as to why the poor spectator cannot get it opened. Of course, you can place the box behind your back and remove the bill, returning it to its owner.
Fun, Inc has not listed these on their website for many years, and most of my internet searches only broght up Sold out messages from other dealers. I also have found that these boxes were "too loose" (where they are secretly gimmicked) to be deceptive. Finding one that is tight deceptive and like new is very difficult now. I have one of these, tested for fit, brand new in the box, which I offer at a reasonable price for this hard-to-find puzzle.