Here is the most authentic account of Origins of Gnyanvapi based on the most ancient source – The Skanda Maha Puranam written by Sri Veda Vyasa Maharshi.
Puranas. Vyasa is also credited with the writing of the eighteen major Purāṇas, which are works of Indian literature that cover an encyclopedic range of topics covering various scriptures. He narrated the Devi-Bhagavata Purana to Parikshit’s son Janamejaya.
Description in Wikipedia goes about Krishna Dvaipayana (Sanskrit: कृष्णद्वैपायन, romanized: Kṛṣṇadvaipāyana), better known as Vyasa (/ˈvjɑːsə/; Sanskrit: व्यासः, romanized: Vyāsaḥ, lit. ‘compiler’) or Vedavyasa (वेदव्यासः, Veda-vyāsaḥ, “the one who classified the Vedas“), is a central and revered sage portrayed in most Hindu traditions. He is traditionally regarded as the author of the Hindu epic Mahabharata. He is also regarded by many Hindus as the compiler of a number of significant scriptures. As a Shaktyavesha Avatar (śaktyāveśa-avatāra) of Vishnu, he is also regarded by tradition as the compiler of the mantras of the Vedas, as well as the author of the eighteen Puranas and the Brahma Sutras. He is one of the seven Chiranjeevis.
The Skanda Purana (IAST: Skanda Purāṇa) is the largest Mukyapurana, a genre of eighteen Hindu religious texts.[1] The text contains over 81,000 verses, and is of Kaumara literature,[2] titled after Skanda, a son of Shiva and Parvati, who is also known as Murugan.[3] While the text is named after Skanda, he does not feature either more or less prominently in this text than in other Shiva-related Puranas.[3] The text has been an important historical record and influence on the Hindu traditions related to the war-god Skanda.[3][4]
The earliest text titled Skanda Purana likely existed by the 8th century CE,[5][6] but the Skanda Purana that has survived into the modern era exists in many versions.[7] It is considered as a living text, which has been widely edited, over many centuries, creating numerous variants. The common elements in the variant editions encyclopedically cover cosmogony, mythology, genealogy, dharma, festivals, gemology, temples, geography, discussion of virtues and evil, of theology and of the nature and qualities of Shiva as the Absolute and the source of true knowledge.[8]
The editions of Skandapurana text also provide an encyclopedic travel handbook with meticulous Tirtha Mahatmya (pilgrimage tourist guides),[9] containing geographical locations of pilgrimage centers in India, Nepal and Tibet, with related legends, parables, hymns and stories.[10][11][12]
This Mahāpurāṇa, like others, is attributed to the sage Vyasa.