Legends and history
Three of them are prominent as narrated below:
First story: Once upon a time Narada (son of Lord Brahma) visited Vindhya parvat (mountain). Narad told Vindhya Parvat about the greatness of Mount Meru. This made Vindhya jealous of Meru and he decided to be bigger than Meru. Vindhya started worship of Lord Shiva to become greater than Meru. Vindhya Parvat practiced severe penance and worshipped parthivlinga (A linga made from physical material) along with Lord Omkareshwar for nearly six months. As a result, Lord Shiva was pleased and blessed him with his desired boon. On a request of all the gods and the sages Lord Shiva made two parts of the lingas. One half is called Omkareshwara and the other Mamaleshwar or Amareshwar. Lord Shiva gave the boon of growing, but took a promise that Vindhya will never be a problem to Shiva’s devotees. Vindhya began to grow, but did not keep his promise. It even obstructed the sun and the moon. All deities approached sage Agastya for help. Agastya along with his wife came to Vindhya, and convinced him that he would not grow until the sage and his wife returned. They never returned and Vindhya is there as it was when they left. The sage and his wife stayed in Srisailam which is regarded as Dakshina Kashi and one of the Dwadash Jyotirlinga.
Second story: King Mandhata of Ikshvaku clan (an ancestor of Lord Ram) worshipped Lord Shiva here till the Lord manifested himself as a Jyotirlinga. Mandhata’s sons-Ambarish and Muchukunda, who had practiced severe penance and austerities here and pleased Lord Shiva. Because of this the mountain is named Mandhata.
Third story: Once upon a time there was a great war between Devas and Danavas (demons), in which Danavas won. This was a major setback for Devas and hence Devas prayed to Lord Shiva. Pleased with their prayer, Lord Shiva emerged in the form of Omkareshwar Jyotirlinga and defeated Danavas.
Adi Shankara’s Cave
Omkareshwar is said to be the place where Sri Adi Sankara met his Guru Govindapada in a cave. This cave can be found even today just below the Shiva temple where an image of Adi Shankara has been installed.