Bonn Kathen is one of the religious festivals for Khmer people and it's the the end of Buddhist Lent. The monks stay for three months in a retreat inside a pagoda and at the end the people all over the country go to local temple to offer them gifts.

Sourced from: https://photocontest.smithsonianmag.com/photocontest/detail/bonn-kathen-in-angkor-wat-cambodia/