Dhosi hill is located on the borders of the Indian states of Haryana and Rajasthan.    It is an extinct volcano, standing alone in the north-west end of the Aravalli mountain range with height varying from about 345 to 470 meters from the surrounding land and 1170 meters from the sea level; it has temple, pond, fort and caves on the top and forest around it. It is part of the Aravalli mountain range, that belongs to the Precambrian Malani igneous suite of rocks and have been dated at 732 Ma BP.

It is one of the most ancient Vedic religious sites in Haryana along with 48 kos parikrama of Kurukshetra, Adi Badri and Kapal Mochan. Besides, the hill is also home to a beautiful water reservoir.

This hill has acquired country wide fame as it is believed that Chavan Rishi practised penance here for many years. On the top of this hill a saucer shaped plain surface is strewn with its ruins of a hill fortress, probably built by King Naunkaran of Bikaner. A temple dedicated to Chavan Rishi decorates the hill. In the memory of Chavan Rishi, a big fair is held on the occasion of Somavati Amavas.

This place is considered most sacred and is regarded as a Tirtha. A Shiva temple, tank and a well exist on the hill. The water of the tank and the well is regarded sacred as that of the Ganga and the Yamuna. Scientifically, the water flows into the pool from three sides of the hill and brings dissolved copper and the essence of various herbs.

There are two temples on the top of the hill, one about 250 years old and the other about 100 years old. In the main temple, the idols of Chavan Rishi, Sukanya, Krishna and Radha stand installed. Besides, an asht dhatu idol of Lord Vishnu lies on Shesh Shayya posture. At some distance from the temple, there still exists a ghufa (cave) where the Rishi is said to have performed tapsya.

It is said that the Rishi used to take a special type of herb known as Chavan Prash. This herb, it is widely believed, is very common here on the hill. Due to constant use of this herb, the Rishi maintained his body well for a long period. It is understood that after his name, a medicine known as Chavan Prash has become very common and popular throughout the country.

Source:

https://en.wikipedia.org/wiki/Dhosi_Hill

https://www.nativeplanet.com/narnaul/attractions/dhosi-hill/#overview