Phra Nang Cave
From my experience, this beach is the most beautiful, white sand, suite for swimming, sun bath, enjoy jogging, etc.The cave is at the end of the beach with a local tale about this cave (I cannot remember the story). You can take about 15 minutes from Railay Beach.
It is believed by local fishermen to be the home of a mythical sea princess. Inside the limestone cave is a collection of strange phallic symbols, offerings and objects believed to help with fertility.