To do this, first obtain the L-rod and equip it. If L-rod turns into "X" sign, then you should not pass and turn around. If L-rod do not turns into "X" sign, then you can pass. Entering the wrong way will cause that the water flow will throw you to the starting position. The more distance between the point where you made a wrong decision and the starting point, the more damage of throwing will significantly increase, which will instantly kill you if the distance was far enough.
This file name is 물귀신(Water Ghost). But, that word may mean figurative meaning. Figuratively meaning : A person who is dragged another person into a trouble when he is in a trouble.