On Sunday 4 April 2021, 46 year old monk Phra Ajarn Manas, on his annual pilgrimage from Nakhon Sawan province, entered Tham Phra Sai Ngam to meditate. This 3 km long cave is on the western edge of the Thung Salaeng Luang National Park, 6 km north of Noen Maprang in Phitsanulok province. While he was in the cave a heavy thunderstorm caused a seasonal sump, 400 m from the entrance, to close trapping him in the cave. As the monk was planning to spend a long time in the cave (he reportedly had some food with him) the alarm wasn’t raised until noon on Tuesday 6 April.