Brahmadvara is the path leading to the realization of Brahman or Ultimate Reality. Dwara means a door or entrance. Brahma Dwara is the door through which one reaches Brahman or emancipation. Brahman denotes the Supreme Being. Brahman is regarded in the ancient Vedic tradition as the material as well as efficient cause of the experiential world. It is the all-pervading being and spirit of the universe. From it everything has emerged and to it everything returns.
According to Hatha Yoga, the place of Mahadeva Shiva is said
to be in the thousand petaled lotus in the skull. The way leading there is
called the Madhya-marga (central way), the mahapatha (big way) or the sushumna
(Hatha Yoga Pradipika III). It is also called brahma nadi or the brahmar-andhra.
Brahmadvara is the opening in the beginning of this way. It is situated at the
base of the spinal column. In all of us, this door to Brahman is closed by the
sleeping Goddess Kundalini. It is located on the kanda (Hatha Yoga Pradipika III 106-107), which is a triangular structure at the base of the spine.
In Sat Cakra Nirupana of Purnananda (verse 10 and Verse 11),
there is a splendid description of how kundalini remains dormant in the adhara
lotus, holding the brahmadvara in its own mouth. By the intense practice of
pranayama and mudras of hatha yoga for a long time, the kundalini is aroused.
It becomes straight, enters the brahma nadi by opening the brahmadvara and
rises up through the six chakras, ultimately merging with Mahadeva Shiva and
brings liberation.