Sowmya Narayana Perumal temple, Thirikoshtiyur, TN where great Sri Ramanuja revealed the moola mantra!!

Thirukoshtiyur Sowmya Narayana Perumal Templetemple@dinamalar
Thirukoshtiyur Sowmya Narayana Perumal TempleTripAdvisor
Sowmyanarayana Perumal Temple in Thirukoshtiyur, near Thirupaththur Tamil Nadu, is  quite popular and is dedicated to Lord Vishnu. It is a significant Divyadesa Shetra glorified in the Divya Prabandham, the early medieval Tamil canon of the tamil Azhwar saints from the 6th–9th centuries AD.  The main deity is  Sowmyanarayana Perumal and his consort is Lakshmi as Thirumamagal.  This temple assumes social and religious importance because it was here the great Vaishnava philosopher Sri Ramanuja  not  only expounded, the  Vaishnavadatta philosophy but also preached the holy ashtakshra "Ohm Namo Narayana" to all people irrespective of their caste. Thus he became the first  social reformer in South India setting aside the caste differences, etc., several  centuries ago. Even today he still remains the greatest  social reformer and gives the right meaning to basic worship of God, ie., people regardless of caste,  creed and birth  can chant Narayana  mantra and before God everybody is equal. This temple follows Vaishnavite tradition of Thenkalai Samprathayam  that follows  Vaikasana aagama
Thirukoshtiyur,Sowmyanarayana PerumalDivine Traveller
Sowmyanarayana Perumal is said to have appeared as Narasimha  to the Devas, the celestial deities before killing the demon king Hiranyakshipu.
Thirukoshtiyur temple, Narashimhar. Tamilnadu Tourism
When Vishnu was  about  to take the Narasimha avatar to annihilate  the demon king Hiranyakashipu, Devas were very anxious to see his new Avatar before he would take it.  So, lord finally agreed and showed them the avatar. The vision was so mesmerizing, the Devas and sages requested Lord Vishnu to show them more. Thus lord Vishnu appeared in three 
forms of standing, sitting and resting posture at Thirukoshtiur. Since Vishnu showed his form  through the  hardship (in Tamil: Thirukkai) of Devas, the place came to be known as Thirukoshtiur
Half human,half lion, Narashimha avatarDolls of India
This temple follows Six daily puja protocols  and holds many annual festivals  among which which the float festival during the Tamil month of Masi (February–March), Navrathri during September–October and Vaikunta Ekadasi during Margazhi (December–January)  are significant. The temple is maintained and administered by Sivaganga Devasthanam.

The temple covering 2 acres of land has a 5 tier entrance gopuram. The temple is enclosed within 
the boundary walls made of granite.  The main sanctum houses the image of the presiding deity, Uragamellayan Perumal in reclining posture on a serpent's coiled bed - Adishesha similar to that of Srirangam Ranganathaswamy temple.  Also present are the images of Sridevi and Bhudevi. There  are two life size images of Narasimha, the avatar of Vishnu. One of them is shown holding the demon Hiranyakshipu and other slaying him.

Here, the festival deity is  Sowmya Narayana Perumal  and the idol is made of panchaloha (a combination of many metals, including gold). 
The vimana, the shrine over the sanctum is Ashtanga in architecture style, which has eight parts. It is a rare piece of Hindu  temple architecture. Though the Dravidian architecture is followed here, the Astanga Vimana is a rare style. Here, the vimana raising to a height of 25 m (82 ft), is taller than the gopuram of the temple, such a  feature is seldom found in Dravidian temples.

As for the shrine of Lord's consort, Thirumamagal it is located to the south of the main shrine. Close to the sanctum are the small shrines dedicated to Sri Rama, Sri Krishna, Andal, Manavala Munigal, etc. The shrines of Garuda, Anjaneya, Ramanuja, Vedanta Desika and Azhwars are  in the second prakara. A rare feature in a Vishnu temple is the presence of Shivalinga Lord Subramanya and Vinayaga -

Sri Ramanujar. Divyadesams
Thirukoshtiyur is the birth place of  Nambigal, the mentor of Ramanuja.  He taught Sishya Ramanuja  the gospel / moola mantra Ohm Namo Narayana and instructed him not to reveal it to anyone. The very mention of narayana means, you will get salvation and mukthi and you wont be troubled by rebirth. Ramanuja made up his mind to let everybody know about this mantra. Besides breaching his Guru's instruction, he risked his own life, climbed the tall tower  and loudly revealed the mantra to all - no caste discrimination.  His Guru. Nambigal, though taken aback, was pleased with his spirited appeal   and commitments of Ramanuja and named him Emperumanar (meaning my superior). Later a life size image of Ramanuja was housed in the Ashtanga Mandap of the temple. Thus,  at this temple Sri Ramanuja became the first social reformer, showing the way to salvation to all people.

The  positioning of sub-deities in this temple is almost similar to those at Appakkudathaan Perumal Temple at Koviladi, Veeraraghava Perumal temple at Thiruvallur, Rajagopalaswamy temple at Mannargudi and Rangantha temple at Srirangapatna.

02. It is to be noted that the Ashtanga Vimana that we have here in this temple, is found in only three places, namely, the Uthiramerur, Koodal Azhagar Temple and Cheranmadevi temples.