Phnom Kulen ("Mountain of the Lychees") is the holy mountain of the Khmer people, located about 50 kilometres northeast of Siem Reap. It is the source of the Siem Reap River — and thus the hydraulic source of Angkor — and is one of Cambodia's most important pilgrimage sites, visited by thousands of Cambodians on weekends and public holidays. The mountain contains a reclining Buddha carved from a large sandstone outcrop, a waterfall that is a popular swimming spot, and the river carvings of Kbal Spean further downstream.
The road to the summit is steep and the mountain is a national park with an entry fee. It is most rewarding on a weekday when the crowds are smaller. The combination of sacred significance, historical importance, waterfall, and forest makes it one of the better full-day excursions from Siem Reap. Note that the mountain is closed on certain religious days. Hire a guide or arrange a tour through a Siem Reap operator rather than attempting it independently without local knowledge.