A tomb is a sealed room for what is over, so tradition reads it as the past kept closed — memories, grief or ancestry held in stone. Entering one is seen as going down into what has long been kept shut.
When this appeared in your dream, what were you feeling?
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.