Thirunallar is very famous for the shrine of Lord Shani (Saturn), which is near karaikal, Pondicherry state. This temple is within the temple dedicated to Lord Darbharanyeswarar. As per myth to this temple, King Nala of Nidadha kingdom married the beautiful princess of Vidharbha,Dhamayanthi, in a swayamvaram arranged by the king and Lord Shani was desirous  of marrying Damayanthi and since Nala married her, he became jealous and furious with him.
As is the nature of Shani, if Shani enters into some one’s life, they suffer ill health, misfortunes and downfall in their life and Since Nala was very pious and never wavered from dharma, Shani could not get hold of him to trouble him. After a few years, Nala washed his legs to perform his morning pooja, did not wash his feet properly. He left one of his heels dirty and dry while cleaning rest of his feet. Shani was waiting for an opportunity all these years. Suddenly he entered onto him through this dry patch on his heel.
Due to Shani’s bad influence, Nala lost his kingdom in gamble. He also lost all his poverty. He became a pauper and started wandering around the streets with his family and he sent his sons to his uncles’s house. Afterwards he went into a forest with his wife. Due to Shani’s high influence, he also left his wife in a lurch in the dark forest and went away. Later, Dhamayanthi was rescued by a king and was escorted her back to her parent’s kingdom. Meanwhile, Nala while wandering in a forest rescued a big serpent called Karkodan, from a forest fire. Instead of thanking him, the serpent bit Nala. By the venom of the snake, Nala turned ugly. The serpent
Karkotan said that this transformation is for a reason. It also gave Nala a cloak made of serpent skin and asked to wear that in an appropriate time and it disappeared.
Meanwhile, Damayanthi, fretting for loss of her husband, asked his father to arrange for another swayamvaram. She has a hope that Nala would come back. Nala changed his name to Vagunan. He became employed as a charioteer to king Irudhupannan who also came to the Swayamvaram with Nala as the charioteer. As Nala was not allowed to participate in the swayamvaram, he went to the backyard and into the kitchen, where he saw his children and started playing with the children. Damayanthi who happened to see this recognized this ugly man to be Nala. Realizing that the time has come, Nala wore the cloak given by Karkodan. he
regained his real personality instantly and became the beautiful king that he was. Becoming confident, he defeated king Putkaran. He regained his kingdom all his properties back.

Though he was united with his family and regained his kingdom, he was still feeling depressed and he didn’t know the reason for these depressions. Sage Narada, once visited him and said that his mental agony was due to the influence of Shani. He asked Nala to take a pilgrimage. On his pilgrimage he met sage Bharadwaja in Vrithachalam, a small town in Tamil Nadu. The sage asked Nala to go and pray to Lord Shiva in the name of Dharparanyeswarar to get rid of Shani’s influence.
As soon as he entered Thirunallaru, he bathed in the tank and went inside the temple and Shani realizing that he should not torment Nala anymore and being afraid of Lord Shiva, went inside the temple and his himself in a corner. Lord Shiva, answered Nala and Dhamayanthi’s prayers, bestowed them with all prosperity and happiness and he also found out the hiding Shani. He told him that henceforth everyone entering the temple after worshipping him will also worship Shani and get his blessings. Since then, whoever comes to this shrine and seeks the blessings of
Lord Shani, their influence by Shani is reduced and they are absolved of their miseries.
Tirunallaru is a major temple in India dedicated to Shani God which is similar to Shani Shinganpur in Maharashtra. In Thirunallaru, the temple has a large seven tier rajagopuram. The nanadavanam (temple garden), Kalathinathan temple, sixty three nayanmar idols, a small sanctum for Nalan are seen in this temple. In front of the flagpost, one can see the sanctum of Sri Dharbaryaneswarar, lord Shiva in the form of lingam which is a swayambu (self originated) and it is customary that one
should visit here first. Apart from these, there is a seperate sannidhi for ambal (named as Parameshwari) and Lord Subramanya with Valli and Deivayanai.
The sthala vritcham (the divine plant or tree of that sthala) is Dharba grass (kusa grass) and hence lord Shiva here is called Dharparanyeswarar. To the left of ambal’s sannidhi is the sanctum for Lord Shani who is the son of Suryan’s second wife Sayadevi and he is also called as Saneeswar , Mandhan and Kaari ( as he is black in complexion). The sanctum is small and idol looks beautiful in the oil lamps and he is facing east and in most temples Lord Shani usually faces south. In most idols of Shani have four hands the idol at the Thirunallar Temple has only two hands. Lord Saturn is the main deity of this temple at Thirunallar and there are no other sanctums for the other grahas (planets).