This temple is dedicated to the Hindu god Ranganatha, a manifestation of Vishnu. The presiding deity is a statue of Ranganatha reclining on a huge multiple-hooded serpent, Sesha. This very important Vaishnavite shrine was built by the Gangas in 894 AD.
To see the statue, you’ll have to go inside. I was too distracted by this poor horse loitering at the entrance to bother.