Palani (or Pazhani) is a town and a municipality in Dindigul district, Tamil Nadu. Palani Arulmigu Shri Dhandayuthapani temple dedicated to Hindu war God Kartikeya is situated on Sivagiri hill overlooking the town. The temple is visited by more than 7 million pilgrims each year.

According to Hindu mythology, Sage Narada once visited the celestial court of Lord Shiva at Mount Kailash to present to him a fruit, the gyana-pazham (literally, the fruit of knowledge), that held in it the elixir of wisdom. Upon Lord Shiva expressing his intention of dividing the fruit between his two sons, Ganesha and Karthikeya, the sage counselled against cutting it. He decided to award it to whoever of his two sons first circled the world thrice. Accepting the challenge, Lord Karthikeya started his journey around the globe on his mount peacock. However, Ganesha, who surmised that the world was no more than his parents Shiva and Shakti combined, circumambulated them. Pleased with their son’s discernment, Lord Shiva awarded the fruit to Lord Ganesha. When Kartikeya returned, he was furious to learn that his efforts had been in vain. He left Kailash and took up his abode in Palani hills. It is believed that Karthikeya felt the need to get matured from boyhood and hence chose to remain as a hermit and discarded all his robes and ornaments. He went into meditation to know about himself.

The Dhandayudhapani Temple dedicated is regarded as one of his Arupadai Veedu (Six Battle Camps). The idol of the Muruga in Palani was created and consecrated by sage Bogar, one of Hinduism’s eighteen great siddhas, out of an amalgam of nine poisons or navapashanam. The Garbagriham is surmounted by a gold gopuram and the walls of the Garbagriham have numerous stone inscriptions describing offerings made by devotees to the temple. A temple is dedicated to Muruga near the foot of the hill by the name of Thiru Avinankudi which actually forms a part of the six abodes of Muruga (Arupadaiveedu).

Besides regular services, days sacred to the god Subrahmanyan are celebrated with pomp and splendour every year, and are attended by throngs of devotees from all over South India. Some of these festivals are the Thai-Poosam, the Pankuni-Uththiram, the Vaikhashi-Vishakham and the Soora-Samharam. Thai-Poosam, which is considered, by far, the most important festival at Palani, is celebrated on the full moon day of the Tamil Month of Thai (15 January-15 February).

Pilgrims after first having taken a strict vow of abstinence, come barefoot, by walk, from distant towns and villages. Many pilgrims also bring a litter of wood, called a Kāvadi, borne on their shoulders, in commemoration of the act of the demon Idumban who is credited by legend with bringing the two hills of Palani to their present location, slung upon his shoulders in a similar fashion. Others bring pots of sanctified water, known as theertha-kāvadi, for the priests to conduct the abhishekam on the holy day.People of Karaikudi, bring with them the diamond-encrusted vél or javelin, of the Lord from His temple at Karaikudi.

Source

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

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

http://www.tntemple.org/arupadai.html

http://www.livechennai.com/detailnews.asp?newsid=9832&nav=n

http://palani.org/palani_pada_yatra.htm