Vaidyanatheshwar, believed to be the fifth of the twelve Jyotirlingas, is located at the Baidyanath Dham (also called Baijnath Dham) in Deoghar District, Jharkhand.
Origin Story: According to the Koti Rudra Samhita of the Shiva Purana, Ravana, a devotee of Shiva, meditated on Mount Kailash for years hoping to bring Shiva to Lanka. When his prayers went unanswered, he began cutting off his own heads one by one and offering them into a sacrificial fire. Moved by his devotion after nine heads, Shiva appeared, restored Ravana's heads, and agreed to let him carry his Atmalinga to Lanka - on the condition that wherever Ravana set it down, it would remain permanently.
Worried about a demon wielding such power, the gods conspired to stop him: Lord Varuna gave Ravana an urgent need to relieve himself, and a cowherd (secretly a disguised deity) was asked to hold the linga meanwhile. As it grew impossibly heavy, the cowherd set it down and vanished - and when Ravana returned, he could not budge it from the ground, however hard he tried, and had to leave without it.
Because Shiva's act of healing Ravana's heads gave him the name Baidyanath - "vaidya" meaning doctor - the site became known as a place of healing, later also called Baijnath after a local hunter devotee named Baiju. The Matsya Purana refers to it as Arogya Baidyanath, a sacred place where Shiva and Shakti cure incurable diseases.