Wikipedia
Dahara-vidya or 'the knowledge of Brahman within', is mentioned in the Chandogya Upanishad and the Taittiriya Upanishad. In this Upasana the sadhaka concentrates on Brahman (the Universal Self) in the cave of the heart. It is one of the thirty-two vidyas of the Upanishads taught in Vedanta, in which vidya Brahman is perceived as the imperceptible ether within the heart. This vidya occurs in the 8th Chapter of the Chandogya Upanishad. where it is taught that the abode of Brahman is the small lotus that is here in this city of Brahman, what is there in the small space within the lotus is to be searched out. This vidya explains the identity of the external and the internal, the objective and the subjective, the macrocosmic and the microcosmic, the universal and the individual, Brahman and the Atman.