Don't Miss in Similan Islands
Whether you're a snorkeler or an experienced diver, this is a great spot for marine life. There are both shallow reef and boulder areas, as well as deep-diving opportunities. The water is very clear -- although along with sharks, barracudas and triggerfish, we also encountered some pieces of plastic bags when snorkeling.
You can also hike the trail (which begins behind the park buildings) up to the rock crowning Koh Similan. It gets a bit steep and rough toward the top, so we don't recommend attempting it in flip-flops. You'll get fabulous views of the sea and probably of your ship at anchor, too.