The strange box is a discontinued item that was given to players by the Mysterious Old Man. When opened, it presented the player with a puzzle; they had to pick which shape held which number, or vice versa, on a spinning box. Upon completing the puzzle the player received coins, gems (sapphire, emerald, ruby, or diamond) or a half key.
Ignoring the strange box resulted in spawning of even more strange boxes. The strange box only stacked when there were no available spaces for it to spawn another box into. Casting high or low alchemy on the box, dropping it, or banking it also caused another box to spawn.
If the player received the strange box when they had a full inventory, the old man instead teleported them to a maze.
Effective on the 25 February 2009 update, all player-owned mystery boxes were automatically converted to Random event gifts and the Mysterious Old Man stopped giving them to players, which made the boxes a discontinued item.
- The strange box used to be a colour-based random event; for example, it may ask "Which shape is red?" or "What colour is the square?". This was changed in an update on 30 January 2006 because colour-blind people were unable to complete the event. 
- According to the Mysterious Old Man, he bought a strange box from a toyshop in the Eastern Lands, a place known for its magical toys. However, he soon noticed that they multiplied constantly. When he ran out of room to keep the numerous boxes, he decided to give them away to adventurers. Of course, this did not stop their multiplying.
- ^ Jagex. "Runesquares, Harpie Bugs and new potato recipes." 30 Jan 2006. RuneScape News.