The whole hill is sacred. It is Shiva himself. Just as we identify ourselves with a body, so Shiva has chosen to identify himself with this Hill - Bhagavan Sri Ramana Maharshi
This books by Sita Kangovi gives a very beautiful insight to Arunachala, its importance and the Saints who were 'Ambassadors of light' - Arunagirinathar, Guhai Namashivaya, Ishanya Deshikar, Seshadri Swamigal and Ramana Maharshi