Why did Indonesians flock to a remote mountain to have sex with strangers? Gunung Kemukus is a hilltop Islamic shrine in Java where, every 35 days, Muslims from across Indonesia arrive to conduct a ritual that involves adulterous sex. As darkness shrouds the hillside, candles are lit and people sit on mats around the sacred dewadaru trees and the twisting roots of massive fig trees. The single grave here is believed to hold a legendary prince and his stepmother. Legend has it that they ran away together and lived at Gunung Kemukus. It is believed that if you do something even more shameful there, like have adulterous sex, then you will be blessed with good fortune. Rebecca Henschke tells the story of this extraordinary ritual. Open Ear features documentaries from producers across the world being rebroadcast by the BBC World Service. It originally aired as a 360 Documentary on ABC Radio National in Australia.Photo: A flower on water, Credit: Thinkstock