Thanksgiving, Christmas and Easter in the West have largely become “Hallmark holidays,” where religious significance has given way to mass commercialism, and an Islamic pilgrimage site in Indonesia is suffering a similar fate. But with one stark difference: Believers are vying for sex, not material gifts or cards.

Every 35 days, thousands of Indonesian Muslims head to a mountain known as Gunung Kemukus to indulge in a mass ritual of adultery. The place is informally known as “Sex Mountain,” and many believe having sex with strangers at the holy site will bring them luck and wealth.

“Praise be to God, after coming here, even though I have a few debts, my business is making a bit of a profit. Even though it’s small, I still give thanks that I’ve received blessings from here,” Mardiyah, a regular visitor who uses one name like many Indonesians, told Australia's SBS network.

According to Javanese legend, a young Indonesian prince, Pangeran Samodro, is believed to have been killed on the mountaintop while he was caught having sex with his stepmother. The spot has now become an Islamic shrine.

“People believe that they committed incest in that place, but before they had finished having sex they were chased by the soldiers of Demak, killed, and buried together,” Floribertus Rahardi, an Indonesian writer who has studied the ritual, told the Global Mail. “From there, the word emerged that whoever can finish off their sex act will receive blessings.”

Islam has strict rules against extramarital sex. In some countries, people are stoned to death for committing adultery. However, at Gunung Kemukus, privately owned karaoke bars and “sex shacks” line the hillside, with men paying women to have sex with them.

“The Islamic religion forbids it, but they don’t want to know that,” Keontjoro Soeparno, an expert on the practice, told SBS. “They’re more interested in profit, they leave religion behind.”

He estimates about half the women who make the pilgrimage to the site are prostitutes. And the Indonesian government, which formally forbids prostitution, turns a blind eye to what takes place at the hilltop. Pilgrims are charged an entry fee of around 5,000 rupiah, or 50 cents, to enter the holy site and stall owners must lease their land from the government. And with many believing that the ritual must be performed seven times at 35-day consecutive intervals, it has become a lucrative business. Commercial sex workers began moving to the area in the 1980s. While sex was performed in the open with only the darkness to keep privacy, the site now is more developed with shacks outside the shrine selling drinks, as well as karaoke places, prostitutes and rooms to rent.

But the ritual isn’t as simple as finding a stranger to sleep with. It must be performed properly to work. When they arrive, pilgrims must first pray at the gravesite and wash themselves in a nearby spring before finding a partner to have sex with. This person must fulfill two criteria: they must be a member of the opposite sex and they can't be your spouse.

When Global Mail reporter Aubrey Belford visited the site in 2012, the man responsible for collecting pilgrims’ entry fees said the vast majority of pilgrims are coming to pray, not to have sex. Indonesia, with a population around 240 million, is the world's largest Muslim-majority country. Conservative Muslim groups have threatened to shut down the site in the past, but police arrived to prevent that from happening.

“This is tourism,” a man identified as Suyono said. "Every component, every element, every layer of society gets something out of tourism.”