Kaya-sadhana (in sanskrit काय, kāya - body, साधन, sādhana - means, instrument)

Kaya-sadhana is a synonym for hatha yoga. Kaya-sadhana is a practice aimed at understanding the identity of one's human body (vyashti-pinda) and the cosmic body of Shiva (samashti-pinda), as well as the unity of Atma, Paramatma and Jivatma. Through the attainment of the Self in the body, the yogi can comprehend the identity of the body and the universe. Kaya-sadhana leads an adept to an equal all-pervasive state of consciousness, which is capable of revealing within itself everything that is in the macrocosmic universe.

According to the views of the Naths, man is like Shiva in his nature at the level of the soul and body. Just as Shiva, despite his manifestation in the world of forms as Saguna Shiva, doesn`t cease to be eternal, so the soul does not cease to remain eternal, transcendent, being in the body. In kaya-sadhana, enlightenment is acquired not only at the level of the mind, but also in the body, because all tattvas are perceived as manifestations of Shiva consciousness. It is at the level of the "coarse" phenomenal world that the greatness of the Divine consciousness can be fully discerned. The body and spirit of the yogi fuse into one single state, which is all at once and is outside the metaphysical extremes of the manifested (saguna) and the unmanifested (nirguna). Kaya-sadhana leads to the realization of jivan-mukti state within the relative being.