Arwad (also spelled Arwad or Ruad) is a small island just off the coast of Tartus, reachable by boat in about 15 minutes. It is the only permanently inhabited island on the Syrian coast, and one of the oldest continuously occupied islands in the world — Phoenician, Greek, Roman, and Crusader rulers each left their mark.
There are ruins of a castle near the west coast that you can wander around freely. Locals claim it was built by Alexander the Great, though the Crusaders substantially rebuilt it. The island's narrow alleys and old sea walls and the small harbour make for an atmospheric hour or two. You do not need to stay overnight — accommodation on the mainland in Tartus is easier and more practical.