Kundalini is the female principle Shakti, the conjoint of which is Shiva, the male principle. Kundallini is in the shape of a Serpent, coiled three and half times and that is the active energy in its dormant condition. Each human being has an Ardhanareeshwara within himself. Just as positive and negatives within a magnet, they stay at poles while on conjoining they are creative. Kundalini stay coiled within the Moladhara which is situated at the base of spinal cord in the triangular bone called Sacrum. Every religion scripture has mention about this Kundalini and its awakening.
Kundalini has a triangular head and when aroused with meditation and yoga, it puts its head up thus opening the Sushumna Nadi. Like a serpent it now moves upwards through Sushumna Nadi towards Sahasrara chakra. It ascends through the Bhu tattva in Mooladhara, Apa Tattwa in Swadhistana, Agni Tattwa in Manipura, Vayu Tattwa in Anahata and Akasha tattwa in Vishuddi to raise to the Ethereal levels of Agya Chakra and finally transcending the ethereal levels it reaches the Sahashrara, which is also known to be the abode of Sadasiva.
Along the way Kundalini needs to break through or untie three Granthis in the Sushumna Nadi. Granthis are psychic knots or blockages and are mostly the major synapses.
Brahma Granthi is the first major block blocking the flow from first chakra Muladhara upwards to others. This is related to bondage of desires.
Vishnu Granthi, the second know blocks the movement of Kundalini from the third chakra Manipura to the fourth chakra Anahata (near heart). This knot is related to bondage of our actions.
Third and final knot is the Rudra Granthi. It blocks the flow beyond the sixth chakra between the eyebrows, ajna/agya chakra, upwards towards sahasrara. This is related to bondage of thoughts.
After coursing through Sushumna Nadi, Kundalini finally reaches the crown of head where we have Sahasrara chakra. When the union happens, we get to experience the Absolute. According to my Guru, “this is the stage when you suddenly feel enlightened. This is the absolute height of spiritual realization. And this realization and enlightenment comes in bursts. These burst moments can be very peaceful and motivating too. You might get flash realization about different aspects of divine knowledge. It’ll show you the truth of the world and about you, and how it’s not the way it appears externally. It is the stage where now you get motivated to continue on the path.”