Being underground is read as going below the surface of everyday awareness, into the hidden and the half-forgotten. Tradition sees it as a journey into the unconscious, both uneasy and revealing.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.