One of Thailand's wildest, remotest corners, the 'Emerald Triangle' is where the Thai, Lao and Cambodian borders converge. Most people visit this little-known 686-sq-km national park to see a pair of waterfalls, but there's some good stargazing and trekking too. For the latter, you must go with a ranger and it's best to call and arrange this before you arrive. You must have your own vehicle to get here.