Tiruvannamalai is a temple town and a major pilgrimage centre in Tamil Nadu. The Annamalaiyar Temple is the most prominent landmark of Tiruvannamalai. Shiva is known by devotees as Annamalayar or Arunachaleswarar and Parvathi as Apitakuchambaal. This is believed to be the largest temple in the world dedicated to Shiva.
The temple complex covers an area of 25 acres, and is one of the largest temples in India. It houses four gateway towers known as gopurams. The tallest is the eastern tower, with 11 stories and a height of 66 m (217 ft), making it one of the tallest temple towers in India. The temple has numerous shrines, with those of Annamalaiyar and Unnamulai Amman being the most prominent. The temple complex houses many halls; the most notable is the thousand-pillared hall built during the Vijayanagar period.
The Annamalaiyar temple is one of the Pancha Bhoota Stalas and here Shiva is said to have manifested himself as a massive column of fire, whose crown and feet could not be found by the Hindu gods, Brahma and Vishnu. Aathara Stalas are Shiva temples which are considered to be personifications of the Tantric chakras of human anatomy. The Annamalaiyar temple is called the Manipooraga stalam, and is associated with the Manipooraga chakra. The temple is revered in Tevaram, the Tamil Saiva canon and classified as Paadal Petra Sthalam, one of the 276 temples that find mention in the Saiva canon.
It has two big tanks named as Brahma Theertham and the other as Siva Ganga Theertham.
The most important festival of the Annamalaiyar temple is celebrated during the Tamil month of Karthikai, between November and December, concluding with the celebration of Karthikai Deepam. A huge lamp is lit in a cauldron, containing three tons of ghee, at the top of the Annamalai hills during the Deepam.To mark the occasion, the festival deity of Annamalaiyar circumambulates the mountain.
Every full moon, tens of thousands of pilgrims worship Annamalaiyar by circumambulating the Annamalai hill barefoot. The circumambulation covers a distance of 14 kilometres (8.7 mi), and is referred as Girivalam. According to Hindu legend, the walk removes sins, fulfils desires and helps achieve freedom from the cycle of birth and rebirth.
Tirumalai is an ancient Jain temple complex in the outskirts of Tirvannamalai that houses three Jain caves, four Jain temples and a 16 feet (4.9 m) high sculpture of Neminatha dated from the 12th century and the tallest Jain image in Tamil Nadu. The Ramana Ashram and ashram of Yogi Ramsuratkumar, located around the Annamalai hill are popular attractions of Tiruvannamalai.
Source:
https://en.wikipedia.org/wiki/Tiruvannamalai
http://www.thiruvannamalai.in/tiruvannamalai-temple/Arunachaleswarar-temple.html