Bordered by Laos and Cambodia on three sides, the tableland of northeast Thailand, known as Isaan , is the least-visited region of the kingdom and the poorest, but also its most traditional. Most northeasterners speak a dialect that's more comprehensible to residents of Vientiane than Bangkok, and Isaan's historic allegiances have tied it more closely to Laos and Cambodia than to Thailand. Between the eleventh and thirteenth centuries, the all-powerful Khmers covered the northeast in magnificent stone temple complexes, which can still be admired at Phimai and Phanom Rung . The mighty Mekong River forms 750km of the border between Isaan and Laos, and there are five points along it where foreigners are allowed to cross the border . The river makes a popular backpackers' trail, not least because of its laid-back waterfront guesthouses in Chiang Khan , Sri Chiang Mai and Nong Khai . Inland scenery is rewarding too, with good hiking trails at the national parks of Khao Yai and Phu Kradung .