The golden triangle is a large geographic region including parts of Myanmar, Laos, and Northern Thailand. This region has infamy as one of the largest sources of opium production in the world, especially during the 2nd half of the 20th century.
The center of the golden triangle is a point where the Ruak river converges with the Mekong river. As national borders, these rivers bring together the countries of Thailand, Myanmar and Laos at a single point.
It is possible to take a short boat ride across to Laos – no visa is required, and your passport is held in safety on the Thai side of the Mekong river. On the other side there is a small market of minor interest, but the boat ride itself is quite fun and provides a good view of the banks on both sides as well as passing cargo boats.
Mae Sai is a border town at the northernmost point of Thailand and has some interesting markets, so this is sometimes included as a point of interest in itineraries.
The convergence of Thailand, Myanmar & Laos on the Mekong River.
Mekong River Cruise
Choui Fong Tea Plantation
Hall of Opium Museum
Mae Sai Border Markets
The original museum at the golden triangle is 101 House of Opium. There is also a new museum called Hall of Opium.