JUST before midnight, the monks were still arriving. Dressed in long, flowing white robes, they resembled fireflies as they rode through the darkness on their motorbikes, descending on the towering temple at the heart of the Cao Dai holy land in southern Vietnam. Many were attending their fourth service of the day.

Removing his sandals and smoothing down his robes, Vo Huu Nghia, 60, who had befriended me that day last year, joined them. He silently entered the cavernous temple and, finding a spot, knelt down and began to chant his prayers. Above him were the serene faces of Jesus, Confucius and Buddha, while a giant all-seeing eye stared down at the few hundred worshipers.

“We are Vietnamese, this is our religion,” Mr. Vo told me later in halting English.

For 70 years this elaborate, dragon-adorned temple outside the small city of Tay Ninh, about 60 miles northwest of Ho Chi Minh City (formerly Saigon) near the Cambodian border, has been the center of Cao Dai, which has five million adherents. While it is not the country’s dominant religion, it has the distinction of being its largest homegrown one.

Every year tens of thousands of visitors, pilgrims and tourists, visit the temple to worship or simply to gaze in awe at its vaulted ceilings, vibrant color schemes and praying masses. And then there’s its unusual collection of saints, prophets and religious iconography, which in range, kitsch and spectacle presents an impressive cross-section of religious and aesthetic styles. But that’s befitting a religion that aims to unite all of humanity through the common vision of an individual creator — the same God honored by most major religions. The protagonist of Graham Greene’s “Quiet American” (1955) described the temple like this: “Christ and Buddha looking down from the roof of a cathedral on a Walt Disney Fantasia of the East, dragons and snakes in Technicolor.”