Zamling Chisang also known as Universal Prayer Day is to celebrate Guru Rinpoche's subjugation of the local deities. It's celebrated on 15th day of the fifth month on Tibetan lunar calendar.
It is marked by extensive offerings, especially Tibetans people go to the tops of local mountains to burn incense and hang prayer. And also in JCI we consider it as biggest ritual, all the nun gather for burn incense (sang) and prayer chanting.