Trimbakeshwar temple is associated with quite a few legendary stories. A sage named Gautam Muni resided on the Brahmagiri Hills with his wife Ahilya. By dint of his sheer devotion, the sage earned from Lord Varuna a bottomless pit from where he could receive inexhaustible supply of grains and of food. The other rishis grew envious of his unending fortune, and devised a plot by pushing a cow to enter the granary, thereby letting it to die, despite attempts by Gautam Rishi to ward it off with a bunch of 'Durbha' grass. Therefore, Gautam Rishi worshipped Lord Shiva by asking him to send the Ganga down to his premises, for purification. Extremely pleased with his devotion, Shiva requested Ganga to flow down below to Gautam's place, and the river flowed. Ganga was asked to stay there eternally for the betterment of the people. Consequently, all the Gods were all praises for Gautam Rishi, Ganga and Lord Shiva.
On everybody's request, Lord Shiva resided by the river Gautami by the name of Trimbakeshwar (one of the Jyotirlingas). Curiously, the locals prefer to call the river Ganga and not Godavari. All the heavenly Saints promised to come down to Nasik, once every 12 years, when Jupiter resides in the zodiac sign of Leo. A grand fair is organized (Sinhastha Kumbh Mela), and the devotees take a must dip in the Gautami Ganga, to seek the Lord's blessings. Hindus believe that the Trimbakeshwar Jyotirlinga is the one that fulfills one's desires and frees one of sins and miseries.
Another popular legend behind Trimbakeshwar temple is the legend of 'Lingodbhava' manifestation of Shiva. The story goes that once Brahma and Vishnu searched in vain to discover the origin of Shiva, who had manifested himself as a cosmic column of fire. Brahma lied that he had seen the top of the column of fire and was hence cursed that he would never be worshipped on earth. In turn, Brahma cursed Shiva that he would be shoved to the underground. Therefore Shiva came down under the Brahmagiri Hill in the form of Tryambakeshwar. Trimbakeshwar Temple is the only place where the 'Shivalinga' is not on the outside, but it's inside the floor.
Some scholars are of the view that Goddess Parvati also came down along with Lord Shiva. The place is therefore called Tryambakeshwa (three lords). Others believe that the place is so called because of the presence of three Shivlinga of Brahma, Vishnu and Mahesh. Amongst the three lingas, the Shivlinga of Lord Mahesh has unending flow of water.
Trimbakeshwar temple is a very ancient shrine, though the current structure is credited to the reconstructional efforts of Peshwa Bajirao in the mid 18th century. The entire temple is made of black stone, in the Nagara style of architecture and is enclosed within a spacious courtyard. The sanctum that is internally a square and externally a stellar structure, houses a small Shivalingam-Tryambaka. The sanctum is crowned with a poised tower, embellished with a giant Amalaka and a golden kalasha. In front of the garbhagriha and the antarala is a mandap with doors on all four sides. Three of these doorways are covered with porches and the openings are ornamented with pillars and arches. Curvilinear slabs rising in steps form the roof of the mandapam. The entire structure is bejeweled with sculptural work featuring running scrolls, floral designs, and figures of gods, yakshas, humans and animals.
The shivalingam is seen in a depression on the floor of the sanctum. Water continuously oozes out from the top of the shivalangam. Usually, the lingam is covered with a silver mask, but on festive occasions it is adorned with a golden mask with five faces, each with a golden crown covering it.
The place is also famous for its religious 'Vidhis' observed, like- 'Narayan-Nagbali', 'Kalsarpa Shanti', 'Tripindi vidhi' etc. 'Narayan Nagbali' puja is exclusively performed at this temple only. It is considered a very sacred puja to fulfill one's desires, held for three days. Trimbakeshwar temple also has a good number of Brahmin houses and is also a centre for Vedic Gurukuls. It also has 'Ashrams and 'Maths' devoted to "Ashtanga Yoga" (the Hindu art of Living).