The other one, Koh Samet, is located a bit more to the South, 1 hour away by car plus 1 hour by ferry. Although there are several beaches with bungalows where to spend the whole weekend, we've only been there on one-day trips.
The first time, we booked a tourist package with taxi, transportation to the island and food, but the truth is that we found it a little bit expensive; so, the second time we decided to go there on our own: a Purac's driver took us to the pier and, once in Koh Samet, we took a pickup to a beautiful isolated beach. Everything was going fine until we started to discuss about the price of the ride. We knew that the driver wanted to charge us more than the standard price and we weren't willing to pay that amount of money. He didn't have any chance but taking us to the beach but, as a good Thai man, he got angry and made his best to scare us by driving in a very madly way. We had such a bad time! Obviously, in that afternoon we called another taxi driver to pick us up and we didn’t dare to negociate the price. We even tipped him!
By the way, that beach in Koh Samet was wonderful and, the food, delicious!!