Finding the giant mole is very easy if you know how to. Simply dig near a mole hill in Falador park with a spade, and you will be ¨transported¨ inside a dark tunnel. Since the tunnel is dark, you will need to bring a light source in order for you to be able to navigate it and not die.  Once you are inside the tunnel, just look at the arrows on your mini map if you have the Falador shield and go there. If you do not have the shield, you will have to look around by running around in the tunnels looking for it. Its spawn point is in the middle, so start there.