Koh Kradan is by far the most stunning and unspoilt island I have been to in Thailand. Seven Seas is one of the best places to stay on the island, with lovely villas. If you have cash to splash go for one of the beach villas overlooking the water, but if on a tighter budget the rooms are very nice and a fraction of the price. The hotel is quite simple, and unpretentious, service was a little hit and miss but the food was delicious. The sea is stunningly clear, as you walk into the water, you are instantly surrounded by hordes of black and yellow tropical fish. It is not the easiest place to get to (which probably helps deter the crowds) - you need to fly to Krabi, travel 2 hours overland then get a boat to the island. Is however definitely worth the effort. I would advise going here for a long weekend, ideally 3 - 4 days if you really want to enjoy it.