The stories in "Nightmare Tales" are often dark and unsettling, and deal with themes such as reincarnation, the afterlife, and the power of the human will. Blavatsky uses the stories to explore her own spiritual and philosophical beliefs, as well as to challenge conventional ideas about reality and the nature of existence. One of the most famous stories in the collection is "The Ensouled Violin," which tells the tale of a violin that is infused with the soul of a dead musician. The story explores the idea of the transmigration of souls and the power of music to connect the living and the dead. Another notable story is "The Cave of the Echoes," which tells the tale of a group of travelers who stumble upon a mysterious cave filled with strange echoes and ghostly apparitions. The story explores themes of illusion and the nature of reality, and suggests that the material world is not the only reality that exists. Overall, "Nightmare Tales" is a fascinating exploration of the supernatural and the mystical, and reflects Blavatsky's deep interest in esoteric and occult subjects. The stories in the collection continue to inspire and challenge readers to this day.