Kecak dance at Uluwatu

Kecak (pronounced: /'ke.tʃak/, roughly "KEH-chahk", alternate spellings: Ketjak and Ketjack), a form of Balinese music drama, originated in the 1930s and is performed primarily by men. Also known as the Ramayana Monkey Chant, the piece, performed by a circle of 100 or more performers wearing checked cloth around their waists, percussively chanting "cak" and throwing up their arms, depicts a battle from the Ramayana where the monkey-like Vanara helped Prince Rama fight the evil King Ravana. However, Kecak has roots in sanghyang, a trance-inducing exorcism dance.

From: http://en.wikipedia.org/wiki/Kecak

I was told that this dance is invented and modified for tourist.