I already know its in relic castle.
You have to go down all the way to the maze which you have to go left(or something. I just kept walking) until you see a long pair of stair and a door. climb up all of those stairs and you have found TM 26. Or if this is too complicated, use http://www.youtube.com/watch?v=9yuX2i5tz9g
You keep going left and earthquake in the maze