Swim With the Elephants
Yes, there is something touristy about impersonating a mahout (elephant trainer) for the day. No, that does not mean you should miss The Anatara Elephant Camp. This is not a joy-ride for the faint of heart - no seat, no saddle, no riens to speak of - this is you, sitting on the crown of an Elephant's skull, death gripping his fuzzy ears - while he nudges you with his trunk because he's wondering when your going to chill out and feed him that piece of fruit you've got in your pocket.
Do it - go for the whole day. It's a once in a lifetime thing and totally worth it.
P.S. Anatara is gorgeous - great pool - stay a while and order khao soi (curried egg noodles). Yum.