Koh Phangan (pronounced closer to "parn-gun" NOT "pan-yang") is a smaller island off Samui and home to the FMP (Full Moon Party). Insane party, lots of fun. Glow-in-the-dark tattoos costing almost as much as real ones. Rows of booth beach vendors selling buckets along with straws, small bottles of spirits and then filled up with energy drinks. As lethal as they sound. Beachside stereo towers blasting House, Trance, Breaks and DnB all night. What was once upon a time considered a fun place to get high is now a very risky place to purchase illicit substances. Shakes are still sometimes sold containing "hetkeekwai" (เห็ดขี้ควาย) - Buffalo-Shit Mushrooms. I've also heard of "hetkeechang" (เห็ดขี้ช้าง) - Elephant Shit Mushrooms but cannot comment on their potency.
As you can imagine the Full Moon Party can get pretty wild. There are always injuries, thefts and plain old silly drunken behaviour. I once saw a very inebriated young white male being taken behind a building by what looked like a hot Thai girl but on closer inspection turned out to be a ladyboy. I assume the guy was oblivious, and hopefully he was not robbed of his possessions along with some of his hetero status.
It's convenient to stay in Haad Rin, then you're only a small walk away from a hot shower and a nice bed (if you can't pick up here then there is something wrong). Rooms book out in advance so be prepared. You can get there by ferry from Samui (approx 200 baht + 1hr ride), or quicker via long-tail boat or speedboat. (anywhere from 600 -1000 baht and 15-30mins). If you take the quicker vehicles always make sure you have access to life jackets, especially at night. Don't ride in any boat that's been overloaded (unless you get a really good price).
If you're not in town during the FMP there's also Half-Moon Parties (along with other various lunar procession parties) so you're always guaranteed a good time. I've heard the rest of Koh Phangan is extremely beautiful and quiet. The diving around Samui and Phangan is also excellent but the serious diver should go further north to a smaller island called Koh Tao.
Koh Tao (turtle island) is basically alcohol and dive shops. If you want to do a PADI dive course do it here. The diving is amazing and the dive shops love to undercut each other so you'll get a great deal. Koh Tao is renowned for sightings of the holy grail of diving, the Whale Shark. The largest fish in the ocean, these massive harmless creatures are amazing to interact with.
So there you have it. These 3 islands are close to each other and the perfect holiday can be had in this area. Just don't get super wasted alone, always be wary of safety precautions and you'll have a blast.
