A whole city hidden under the ground is read as a busy inner life that others do not see. Dream books take it as thoughts, plans or feelings that are living and working out of sight.
Does the traditional reading fit your dream, or did it mean something else to you?
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.