Dhuni

The Nath Dhuni of antiquity is perhaps no different than those of today. A simple and shallow cleft in the ground in which suitable materials are incinerated. The Dhuni is not a simple camp fire. It was viewed by the Nath as a living deity, emblematic as the womb of the Earth Goddess from which all manifestation was generated, sustained, and destroyed.
Although many cultures have sustained a tradition of fire worship, it remains a unique feature of the Naths that it was the site or dwelling place of the Holy Fire which was considered sacred. The ancient but graphic iconography of such a scene is simple. The cleft in the earth represents the womb of the Mother Goddess. This was the Holy Ground upon which the Nath way of life was brought into being, transformed, and regenerated.
Further reading:
Awakening the Nath Dhuni by Sri Kapilnath
Rudra Dhuni by Sri Kapilnath