In 1577, obeying the commandment of her confessor, Teresa of Avila writes her most important work: The Interior Castle. Taking into account her personal experience, in this treatise the author describes the stages through which all people attracted by God go in their encounter with him. The freshness of her language, the force of her symbols, and the constant reference to her experience make The Interior Castle into a thrilling "travel guide." With it on our side, we go into the mystery and wonder of relating to the God who abides in our most intimate being.In order to find what true Christian mysticism is, leaving aside false images, we must go back to the classics, to those authors and works who have shown us a true mystical experience. Among them, St. Teresa and her Interior Castle occupy an outstanding place.