Bali is religiously isolated

Although almost 100% of the indonesian population are Muslim 90% of the resident in Bali are Hindus. The Balinese population (about 4 millions) practice their special form of Hinduism since centuries and settled down in Indonesia even before the Muslims did.

Religion in Indonesia

http://en.wikipedia.org/wiki/Religion_in_Indonesia

Nine Beliefs of Hinduism

The Hinduism in general has nine basic beliefs which are followed by all denominations of this religion. Even though there are several reinterpretations by one of the four subsections (Saivism, Shaktism, Vaishnavism or Smartism) we can say they all follow the same spirituality.

Worldwide distribution of Hinduism

http://en.wikipedia.org/wiki/Hinduism