Often dubbed the heart of Isaan, Khon Kaen has a population between 200,000 and 400,000 (depending on the source), making it one of Thailand’s largest cities. With an enrolment of over 25,000, Khon Kaen University is the biggest in the Northeast. Laos and Vietnam both have consulates here issuing visas in advance — a necessity for travel to Vietnam and required if you want to catch one of the international buses to Vientiane.