The Upaniṣads — the philosophical core of the Vedic tradition, revealing the nature of Brahman, the Ātman, knowledge, action and liberation. The ten principal Upaniṣads together with select minor Vaiṣṇava Upaniṣads.
A short manual on the "yoga of crossing over": how to look, where to seek the inner light, why a teacher is needed. It ends by saying that this vision is rooted not in a technique, but in a teacher.