Southern Laos is less mountainous than the north and centre of the country, which means more arable land and, consequently, denser settlement. Savannakhet and Champasak provinces, dominated by flat river plains along the Mekong, are home to 1.7 million people — roughly one quarter of Laos's total population. The Mekong itself forms the entire western border with Thailand. Its tributaries — the Xe Banghiang, the Xe Don, and the larger Xe Kong — flow east to west across the southern landscape ("xe" meaning river in the southern dialect). At the Cambodian border, the Khone Falls prevent boats from travelling further downstream, making the river an internal boundary as much as an artery. Between the Mekong floodplains and the Annamite mountains that mark the Vietnamese border lies the Bolaven Plateau, rising above 1,000 metres — a fertile, coffee-producing highland of waterfalls and mild climate that straddles Champasak, Xekong, and Saravan provinces.

Ethnic Lao — the Lao Loum, or lowland Lao — are the dominant group along the Mekong plains, practicing wet-rice farming and following Theravada Buddhism. Their culture and language are closely related to Thailand's; more ethnic Lao live in northeastern Thailand than in Laos itself. East of the main river valleys, Lao Theung groups practice shifting cultivation on upland slopes, with communities extending into western Vietnam and northern Cambodia. In the highland areas, Lao Sung peoples — less numerous in the south than in Laos's northern mountains — maintain primarily animist traditions centred on local forest and river spirits. Their languages vary enormously, often unintelligible not just to Lao Loum speakers but to each other. Fluency in Lao, the national language, diminishes as remoteness increases. Southern Laos doesn't fit a single cultural description; it is a region of overlapping communities whose boundaries were drawn more by geography than by any political logic.

Wat Phou — the Angkorian temple complex whose ruins sit 10 kilometres from Champasak and 40 kilometres from Pakse — was designated a UNESCO World Heritage Site for the scale and intactness of its millennium-old stonework. It predates Angkor Wat and shares its cosmological orientation, built on the slopes of a mountain that the Khmer considered sacred. Further south, near the Cambodian border, Si Phan Don — the "Four Thousand Islands" — spreads across the Mekong in a maze of channels, sandbanks, and waterways where the river reaches its widest point in Southeast Asia. The Khone Phapheng Falls, accessible by boat from Don Khon island, carry more water than any other waterfall in Southeast Asia. These aren't isolated attractions. They're part of a landscape that has been continuously inhabited and navigated for thousands of years.

Southern Laos is a transit region as much as a destination — the zone where Laos, Vietnam, Thailand, and Cambodia press against each other along borders that carry histories of war, trade, and migration. The Thai-Laos Friendship Bridge No. 2 at Savannakhet connects to Mukdahan in Thailand; a third bridge links Thakhek to Nakhon Phanom. Border crossings into Vietnam operate at multiple points in Saravan and Savannakhet provinces. Pakse airport is the region's only international entry point, handling flights from Guangzhou, Ho Chi Minh City, and Siem Reap as of late 2024. The Mekong, despite its scale, is not navigable through the south due to waterfalls and dams. Long-distance buses fill the gap, threading between cities on roads that can become impassable in monsoon season. Border officials across the region have a reputation for improvising extra fees — travellers are advised to check recent reviews before crossing.