A treasure hunter is given the clue encased in ice. They must break the ice to retrieve the clue. This is a very simple clue, but very satisfying for the hunter as they attempt to crack their way in.
To make the clue, first water proof the clue. If it is written on paper laminate it or wrap it in clingfilm or a plastic bag. Next fill a freezer proof bowl with water and place the clue into it. You may have to weigh the clue down to get it to settle into the centre of the bowl. Sometimes part-freezing the water before placing the clue in makes this easier.