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When I was in Thailand, I really enjoyed exploring the islands. I was down in
Koh Samui and
Koh Phangan most recently. Koh Phangan is where the infamous Full Moon Party happens once a month. Besides the party, I think that the island is really beautiful and a ton of fun. Also, it's really cheap to stay and live at and very easy to get around. You can either rent a moped or get around on the back of pickup cars (they're the taxis of the island) that drive along the main road of the island. Lots of young Europeans flock there for the party every month and some end up staying longer before or after the party, so you'll be in good company :)
I remember one of my goals would be to ride an elephant. Unfortunately, I didn't hit the right areas to do it, but it would be cool if you found an elephant sanctuary. I think that would be an experience.