This 800m-high extinct volcano dominates Tiruvannamalai – and local conceptions of the element of fire, which supposedly finds its sacred abode in Arunachala’s heart. Devout barefoot pilgrims make the 14km (four-hour) circumambulation of the mountain, stopping at eight famous linga, especially on full-moon and festival days. The inner path is closed for the foreseeable future, but it's possible to circle around on the main road, or climb the hill past two caves where Sri Ramana Maharshi lived and meditated (1899–1922).
The hot ascent to the top opens up superb views of Tiruvannamalai, and takes five or six hours round trip: start early and take water. An unsigned path across the road from the northwest corner of the Arunachaleshwar Temple leads the way up past homes and the two caves, Virupaksha (about 20 minutes up) and Skandasramam (30 minutes). Women are advised not to hike alone, and it's suggested that no one go up after dark due to 'too many drunk boys'. Note that the trail to the top closes a month or two before the Deepam festival, but the caves remain accessible.
If you aren't that devoted, buy a Giripradakshina map (₹15) from the bookshop at Sri Ramana Ashram, hire a bicycle from a shop on the roadside 200m east of the ashram (per day ₹40) and ride around. Or make an autorickshaw circuit for about ₹400 (up to double at busy times).