Why go
Use the central plain as your geographic reference point when planning beyond one city. Siem Reap and Tonlé Sap belong to the lake basin, Phnom Penh sits downstream where major rivers meet, and the Cardamom and Elephant mountains separate much of the Gulf coast from the inland plain.
The full story
Cambodia is shaped around a broad, low-lying basin. Tonlé Sap occupies its northwest, while the Mekong crosses the eastern lowlands on its way toward Phnom Penh and the delta beyond the Vietnamese border. The surrounding higher ground gives journeys out of the basin a different setting: forested eastern plateaus lead toward Laos and Vietnam, the Dângrêk range rises along the northern edge, and the Cardamom and Elephant mountains fill much of the southwest. A narrow coastal strip lies between those southwestern mountains and the Gulf of Thailand. The plain has long supported wet-rice farming and dense settlement, while the lake's seasonal expansion changes the extent of open water and flooded land. This pattern explains why a visit to Angkor, a boat journey on Tonlé Sap and time in Phnom Penh can feel connected, yet a trip to the southwest coast crosses a clear change in terrain. Read the landscape as a basin with several distinct margins, rather than a single flat country.