Baba Harihar Nath Mandir is one of the most revered Hindu temples of Sonepur in Bihar's Saran district. The temple stands near the sacred meeting point of the Ganga and Gandak rivers and is dedicated to the unique combined form of Lord Shiva and Lord Vishnu, known as Harihar. The temple's distinctive Harihar Shivling is traditionally described as having Shiva represented on one part and Vishnu on the other, symbolizing harmony between Shaiva and Vaishnava traditions. According to local religious tradition, the shrine is associated with Lord Rama, while the present temple structure has undergone reconstruction and renovation over different periods. The temple becomes especially significant during Kartik Purnima and the famous Sonepur Mela. Devotees also visit during Sawan and Mahashivratri to perform worship and Jalabhishek.