"Interior Castle" is a spiritual classic written by Teresa of Ávila, a 16th-century Spanish mystic and nun. The book uses the metaphor of a castle to describe the soul's journey toward union with God. It consists of seven mansions, each representing different stages of spiritual growth and deepening intimacy with the divine. In this work, Teresa emphasizes the importance of prayer and contemplation as means to navigate through the mansions. The text serves as a guide for individuals seeking a deeper relationship with God and offers insights into the challenges and rewards of spiritual life.