Phnom Penh lies north to south along the Tonle Sap River and the river provides a natural marker. Your major reference points are the Tonle Sap itself (and the Royal Palace), Wat Phnom, Central Market, Independence Monument, and Boeung Kak Lake.
Along the river is Sisowath Quay. It is here that you will find the Royal Palace, the ceremonial heart of the city. Just near the Palace and the National Museum is one of the primary restaurant and cafe districts. Virtually the whole riverfront is now a series of eateries interspersed with hotels, Internet cafes, and travel agents.
Heading a few blocks west and running parallel to Sisowath Quay is the major artery of Norodom Boulevard. The two major landmarks along this road are Democracy Monument to the southwest of the Royal Palace and Wat Phnom where it ends at the northern end of Central Phnom Penh.
Heading west again across the parallel intersections with Street 51 and Street 63, one arrives at Monivong Boulevard. This is the city's main thoroughfare and is very hectic during the day. Along Monivong, you will find many of the major banks and airline offices. At the northern end of Monivong is the area around Boeung Kak Lake (although the lake itself now represents prime real estate and there are plans afoot to fill it in). This has for a long time been the main backpacker area. Ringing the lake (at present) is a series of very cheap guesthouses and restaurants. To the north, Monivong ends at a large roundabout. This place has historical significance since the nearby French Embassy was where foreigners sheltered in 1975 after the city fell to the Khmer Rouge. Heading east from the roundabout will take you to the Japanese Bridge that crosses to Prek Leap.
Phsar Thmei, or the Central Market, is a huge and eccentric French Art Deco landmark in the center of town between Norodom and Monivong.
Circling the central part of Phnom Penh is Mao Tse Tung Boulevard. Three major arteries radiate out from Monivong to Mao Tse Tung: Confederation de la Russie (Airport Rd.) heading due west passing the southern side of Boeung Kak Lake; Kampuchea Krom Boulevard, which parallels it 4 blocks south; and Charles de Gaulle (turning into Monireth), which takes you southwest out of the city. Sihanouk Boulevard is a kind of inner ring road partially echoing Mao Tse Tung Boulevard to the west and south starting at Independence Monument and Norodom and ending at Confederation de la Russie just south of Boeung Lak Lake.
A lot, but by no means all, of the hotels and restaurants are situated in the area between the Tonle Sap and Monivong, south of Wat Phnom and north of Victory Monument. Between Monivong and Norodom south of Sihanouk Boulevard is a leafy and relatively quiet residential network of streets, called Boeung Keng Kang, where many expats live, and NGOs and international organizations are housed in former French villas. There are also many restaurants and cafes and it is in many ways the most pleasant part of town.
The Tonle Sap: The Heart of a Nation -- The Tonle Sap is the only waterway in the world that changes direction halfway through the year and starts to flow in the opposite direction according to the season. From November to May, Cambodia's dry season, the Tonle Sap flows into the Mekong River, the two waterways converging at Phnom Penh. However, when the monsoon rains begin in June, the Tonle Sap backs up the other way to form what is essentially an enormous natural reservoir. The direction of the Tonle Sap is decided by the pressure of the water from the Mekong, either forcing it back into the Tonle Sap Lake when the river is high or drawing it into its own flow when the river is low. It is a natural safety valve, giving the Mekong natural elbowroom to flow through the delta and on to the sea. Most of the year, the Tonle Sap Lake is relatively shallow. During the rainy season, it increases in area to 16,000 sq. km (6,240 sq. miles) and its depth can reach up to 9m (30 ft.), flooding surrounding fields and forests. The Tonle Sap is the beating heart of Cambodia. It has traditionally provided abundant irrigation for rice while yielding plentiful amounts of fish -- the central sustenance of life for Cambodians.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.