We are faced by the Unconscious, the Void. In developing spiritually there is often a sense of having to go down into the depths to reach understanding. We are being confronted by unknown or perhaps unrecognized negative elements in our own make-up; we have no previous experience by which to judge our actions or reactions. When we dream of a chasm or large hole, we are usually being made conscious of situations that contain an element of the unknown, or are in some way risky. We are going to have to make decisions as to whether to face the risk or withdraw. You might like to consult the entries for Cave, Cliff, Hole and Void.