One of the best museums in all Thailand and almost certainly the most interesting place to visit in the Golden Triangle, the Hall of Opium exhibits the history of opium around the world and in the area, the process of production, the effects of opium smoking and campaigns to eradicate and substitute the crop. There's even a tiny opium plantation inside! The hall describes itself as "edutainment", and indeed this is something of an opium theme park, with the latest in snazzy multimedia exhibits and lots of subtle hectoring about the evils of addiction. To their credit, though, they don't whitewash Thailand's own history at all and even the CIA's exploits are covered in detail. Popular with tour groups and school children. Run by the royal Doi Tung Foundation, with profits going to charity.