The capital of the same-named province, Tay Ninh is situated 95 km northwest of Ho Chi Minh City and is the original home of the Cao Dai religion.
The town itself is a bit of a nondescript affair -- accommodation and eateries are available, but very few travellers choose to overnight here -- primarily because the tours from Saigon are so affordable -- some going for as little as US$2 per person!
The people flock her to see the Cao Dai Holy See -- the great temple of the Cao Dai faith -- which sits a few km outside of town. A garish meld of styles and influences, the temple is dominated by the divine eye which is the religion's representation of God -- for those who are curious, it's a left eye. The temple is done out in hues of pink and baby blues, with a brilliant interior bedecked with eight grandiose pillars wrapped with writhing dragons, and a clouded pastel blue sky that wouldn't be out of place in a Vegas casino -- you really have to see the place to believe it. The faith has built temples all over the region -- especially in the Mekong Delta -- but this is the biggest, brightest and the best.
The Cao Dai beliefs are a curious mix of Mahayana Buddhism, Confucianism and Taoism with a decent dash of home-grown remedies thrown into the mix. The religion came out of activities of the Vietnamese public officer and mystic, Ngo Minh Chieu, who was on the receiving end of revelations from 1919 onwards, culminating in the founding of the religion in 1926. These revelations are believed to have come directly from God. For a belief which once had a standing army of over 20,000 the practices laid out in these revelations are decidedly non-violent -- frequent prayer, veneration of ancestors, non-violence and vegetarianism are all centrepieces.
It's the Cao Dao prayers that forms the key attraction at the Holy See from a tourist's perspective. Ritual prayers are held four times daily with the midday session the most likely one you'll see if you visit as a part of a tour from Saigon. Be aware that while you're permitted to photograph the prayers from the upstairs terrace (where all the tourists are herded) you're not permitted to take pictures of individuals without first asking permission. As with most temples, respectful attire is required -- no singlet tops, shorts, nor, need it be said, bikini tops.
If you decide to visit the temple independently, aim for a prayer session other than the midday one as you'll have far fewer tourists to share the spectacle with.
To reach Tay Ninh from Saigon catch a bus from either Tay Ninh or Mien Tay bus stations in Saigon. The trip will take two to three hours. Once you're in Tay Ninh, walk, or get a xe-om to the temple itself.