ARUNACHALAM

Arunachala refers to the holy hill at Thiruvannamalai in Tamil Nadu, where the Annamalaiyar Temple, a temple of Lord Shiva is located. Every year in the Tamil month of Karthigai (October–November), the Karthigai Deepam (Light) is lit atop the hill. This place is also known by the names Arunagiri, Annamalai Hill, Arunachalam, Arunai, Sonagiri and Sonachalam. It is the most important holy place for people practicing Atma vichara (self enquiry) and one of the 5 main shaivite holy places in South India.
A very early reference to Arunachala can be found in Rigveda, the first of the four Vedas. The composition of the core of Rigveda is usually dated to approximately 1700-1100 BC. In Rigveda, a dispute is described between Brahma the creator and Vishnu the preserver over which of them was superior. In order to settle the chaos that resulted from their argument, Lord Siva is said to have manifested as a column of light, and then, in response to their prayers, taken the form of Arunachala.
Arunachala Mahatmyam says,
"By seeing Chidambaram, by being born in Tiruvarur, by dying in Kasi, or by merely thinking of Arunachala, one will surely attain Liberation."
Another verse in the Arunachala Mahatmyam, translated from Sanskrit into Tamil by Sri Ramana Maharshi says:
"Arunachala is truly the holy place. Of all holy places it is the most sacred! Know that it is the heart of the world. It is truly Siva himself! It is his heart-abode, a secret kshetra. In that place the Lord ever abides the hill of light named Arunachala."