Ravana, the King of Lanka, was an ardent devotee of Lord Shiva. The Shiv Purana says that, once, he had a desire to bring Lord Shiva to Lanka. He went to Mount Kailash, Shiva’s abode, and meditated for years, but could not please the lord. Undeterred, he started cutting off his heads one by one and offering them in the sacrificial fire. He cut off nine of his heads in this manner. When he was about to cut off his tenth and last head, Shiva appeared and stopped him. He was pleased with Ravana’s intense devotion and put his nine heads back again. He also granted him a boon. Ravana expressed his desire to take him to Lanka. Lord Shiva instead gave him a Shivalinga to take to Lanka, but cautioned him that the Linga would get established at the first place that he put it down, and then nobody would be able to move it.
Ravana started for Lanka in his aerial vehicle, Pushpak Vimana. Ravana’s arch enemies, the Devas, decided to put obstacles in his path. While flying to Lanka, Ravana observed that the Sun was setting. He used to never miss his sandhya (evening prayers). He lowered his vimana at a place called Deoghar in modern-day Jharkhand. The Devas saw an opportunity. As Ravana looked around for somebody to hold the Shivalinga while he prayed, he saw a local cowherd boy, who, in reality, was Lord Ganesha. The cowherd agreed to hold the Shivalinga.
As preparation for his prayers, Ravana performed achamana (the ritual of sipping water off one’s palm). Varuna, the Lord of waters, entered his body through the droplets of water. Due to the influence of Varuna, Ravana felt an uncontrollable urge to urinate. He rushed into the nearby forest to relieve himself. As soon as he was gone, Ganesha coolly put the Shivalinga down and left for Mount Kailash. When Ravana returned, he saw the Shivalinga lying on the ground. He tried to pick it up, but no matter how hard he tried, it would not budge. In frustration, Ravana pressed the Shivalinga with his thumb. This left a mark, which is visible to this day, on the Shivalinga. Ravana had to leave empty-handed for Lanka.
The place became known as Baidyanath Dham because baidya in Sanskrit means a doctor, and Lord Shiva acted like a doctor when he restored Ravana’s nine heads. Even today, millions of pilgrims fill Gangajal in their kanwars from Sultanganj and offer it in the Baidyanath temple during the month of Sravana (July-August). Some scholars believe that this is the origin of the Kanwar Yatra, which is now done all over north and central India.