Thailand's least-developed area, the great northeastern region comprising the Khorat Plateau and Mekong Valley is worth visiting for its many attractions and the locals' engaging disposition. The people are Thai nationals whose mother tongue is Lao. They have a distinctive musical tradition and a spicy cuisine, loved by Thais. The Khorat Plateau is an immense, semi-arid tableland punctuated by the cities of Nakhon Ratchasima (also known as Khorat), Khon Kaen, Ubon Ratchathani and Udon Thani. The 'Khmer Culture Trail' - a jewel-like string of Khmer temples dating from the Angkor period - leads east from Nakhon Ratchasima to a point near Ubon Ratchathani.