The Tonlé Sap river changes direction twice a year, and Phnom Penh sits at the point where it happens.
For most of the year the river drains a great lake in the northwest down into the Mekong. Then the monsoon arrives, the Mekong rises faster than the Tonlé Sap can empty into it, and the pressure pushes the smaller river backwards. Water runs north instead of south for several months, and the lake swells from around 2,500 square kilometres to something over 12,000, flooding forest and farmland and becoming one of the most productive inland fisheries on earth.
In late October or November, as the Mekong falls, the flow reverses again. The Bon Om Touk water festival marks the day, with boat races on the confluence and several million people in the city.
The confluence itself — where the Mekong, the Tonlé Sap and the Bassac meet — is called the Chaktomuk, the four faces, and the royal palace looks directly out at it.
What has to be said
Between 1975 and 1979 the Khmer Rouge emptied Phnom Penh at gunpoint within days of taking it, sending two million people into the countryside, and killed something in the region of a fifth of the Cambodian population through execution, starvation and forced labour.
Tuol Sleng, a school converted into the S-21 interrogation centre, and Choeung Ek, one of the killing fields outside the city, are both open. They are not day-trip curiosities. They are documented sites of mass murder within living memory, with survivors occasionally present at Tuol Sleng, and they deserve a full morning, the audio guide, and no photographs of the kind people take without thinking.
Go. Go early, go quietly, and do not schedule anything cheerful immediately afterwards.
The city
Daun Penh and the riverfront hold the royal palace, the silver pagoda, the National Museum and most of the hotels, along the promenade facing the confluence.
BKK1, south, is the embassy and restaurant quarter.
Tonle Bassac has the newer towers and the riverside development.
Koh Dach, the silk island, is a short ferry upriver and is farmland and weaving villages.
The six below are grouped that way.
The riverfront and Daun Penh
By the confluence.
Raffles Hotel Le Royal occupies a 1929 building in gardens with a colonnaded bar that has served the same gin cocktail since the 1930s, a pool among frangipani and a history that runs through the whole of the country's twentieth century. It is the hotel of Phnom Penh.
Raffles Hotel Le Royal
Daun Penh · 5★ · $$$
A 1929 building with a colonnaded bar and frangipani pool
Check availabilityRosewood Phnom Penh sits on the upper floors of the city's tallest tower with a spa, a pool and the confluence laid out below.
Rosewood Phnom Penh
Vattanac Tower · 5★ · $$$
The upper floors of the tallest tower, over the confluence
Check availabilitySofitel Phnom Penh Phokeethra occupies a French colonial building near the riverfront with a courtyard, two pools and gardens.
Sofitel Phnom Penh Phokeethra
Near the riverfront · 5★ · $$
A colonial building with two pools and gardens
Check availabilityBKK1 and the south
The embassy quarter.
Palace Gate Hotel & Resort sits in a converted ministerial building with a large garden, two pools and a spa, a few minutes from the palace.
Palace Gate Hotel & Resort
Near the Royal Palace · 4★ · $$
A converted ministerial building with a large garden
Check availabilityHyatt Regency Phnom Penh occupies a modern property with a spa, a pool and the restaurants of BKK1 around it.
Hyatt Regency Phnom Penh
Daun Penh · 5★ · $$
A spa and pool near the palace and the museum
Check availabilityPlantation Urban Resort & Spa sits in a garden compound with a pool, a small room count and a quieter position.
Plantation Urban Resort & Spa
BKK1 · 4★ · $$
A garden compound with a pool and few rooms
Check availabilityWhat we have left off
The small guest houses along the riverfront and in BKK1 are excluded, and Phnom Penh has a large supply of them at very low prices. They are guest houses rather than hotels.
What to do
Give Tuol Sleng and Choeung Ek a morning, in that order, with the audio guides. Nothing else in the city means much without them.
Walk the riverfront at dusk when the city comes out to exercise, eat and sit, and watch the confluence.
See the National Museum for the Angkorian sculpture, which is better presented here than at the temples themselves, and the Royal Palace next door.
Take the ferry to Koh Dach for the silk weaving, which is done on handlooms under stilt houses and can be bought directly.
Eat. Cambodian food is distinct from Thai and Vietnamese — less chilli, more fermented fish and kroeung herb paste — and fish amok, kuy teav noodle soup and the grilled river fish are the places to start.
Practical notes
Phnom Penh's airport has regional connections; Siem Reap is a five-hour drive or a short flight, and a river boat runs in high water.
November to February is the dry, cooler season and best. March to May is very hot. The monsoon runs June to October and is when the river reverses.
The water festival in late October or November fills the city entirely.
Every hotel bookable in Phnom Penh
Does the river really reverse?
Yes, twice a year. The monsoon-swollen Mekong pushes the Tonlé Sap backwards, swelling the great lake to several times its dry-season size.
Should you visit S-21?
Yes, and with the audio guide. It is a site of mass murder within living memory and it is the context for everything else in the city.
Phnom Penh or Siem Reap?
Both. The capital for the river, the museum and the recent history; Siem Reap for Angkor. Five hours apart.
How many nights?
Three. One for the history, one for the city, one for the river.