The main reason for visiting Ko Muk is to head to the site of the Emerald Cave or Tham Morakot. There are two ways of getting here: by boat at low tide; or for the more daring, by swimming across. However, there's only one access point, namely a long tunnel (which in certain parts is completely blind) dug into the cliff to reach a very pretty white sandy beach where emerald colours are reflected in the water.