Things in the Game: Exit
Once Rich has all the diamonds, the exit will open. Rich then has to get to the exit square to complete the puzzle. Note that when Rich enters the open exit, he is immediately protected, so if there is a monster or other peril after him, he manages to escape.
A rock will roll into an open exit, blocking the exit, so make sure that the rock isn't on the exit when the last gem is taken. A box, however, can be pushed off an open exit.