One of the biggest religious festivals in Cambodia, Pchum Ben, has a wonderful tradition of feeding monks in temples in order to satisfy hungry ghosts. These creatures are believed to have huge stomachs and always remain hungry, so by feeding them people believe they are bringing merit to their ancestors. All devotees are wearing white on this day as a symbol of mourning, Cambodians are carrying lots of food to the temples and are asking monks for blessings.
One of the best places to see the traditions of the Cambodian Day of the Dead is Wat Langka in Phnom Penh. It's one of the oldest and most important pagodas in the city dating back to 1442. In the Siem Reap area, Pchum Ben is celebrated at many temples. You can choose the modern Wat Preah Prohm Rath temple or old Wat Bo temple across the river. Of course, you can also see Pchum Ben rituals at the Angkor Wat. The glorious landmark also attracts many locals who rush there to make their offerings so expect it to be rather crowded.