Interior Castle gives you a look into the mind of one of the most famous "Christian" mystics. Teresa of Avila was a nun in Spain during the Counter-Reformation, which should ring bells for those of us on the Protestant side of the Council of Trent. Although Saint Teresa was clearly a woman of deep humility and a profound power over words, she left behind a questionable work that does little to enlighten the Christian mind to the truths of God's Word and instead offers an approach to prayer based firmly on experience and emotion.
If you are interested in Catholic mysticism, church history, classic literature, or extended metaphor, you may find this book very enjoyable. The narrator, Susan Deneker, does well, reminding the listener though action that narration is a performing art. But if you are seeking to learn more about prayer, developing an experiential relationship with God, or understanding how feelings fit with faith, search for another book. I'd suggest Jonathan Edwards' classic The Religious Affections.
To buy the audiobook, visit ChristianAudio.com (direct link to book information).
To buy the hardcover book, visit Amazon.com.