[throwaway-8c93]

They're not islands in a strict geographical sense, but there are a dozen or so countries which are de-facto islands for any practical purposes - accessible only through large bodies of water, with land borders mostly impassable or crossed so infrequently that they don't matter.

South Korea, North Korea, Finland, Vietnam, several central American countries and others. Even China fits the bill. Not sure how frequent traffic across Thai borders are, but my impression is that SE Asian countries are not very well integrated.