Look up "Cao Dai" in Google or read about it in the Lonely Planet Vietnam book. It still won't prepare you for the "wow!" of entering the Great Temple. There are more "wow" experiences as the faithful enter slowly in their magnificent robes and a different muted "wow" when the quiet repetitive chanting begins from the choir. And these people don't ask the tourists for money for any of this. Not a hint, not even in the car park.