The trench tool digs up dirt for in game secrets. To find the tool you must get to the level named Search of yamashitakas gold and find the lotus flower on a statue inside the palace. Walk up to the front of it and you'll pick it up. After you fall down the hole, go down to the end of the hall into a room with a gold statue. There is a pedsetal. Press X on it and it should say, "YOU HAVE REACHED ENLIGHTENMENT." Then a door will appear to the right and in there is a hammer-like tool.