Kos
Kos is a jewel of an island in the Mediterranean. The main town suffers from numerous stag and hen does, but further out the island is peaceful. There are a range of ruins scattered around the island and in the north a geothermic spring feeds a pool creating a natural hot tub.
You can rent a car, a bike or what amounts to a dune buggy. My driving of which caused my travel companion to swear to never get in one again with me. There are a lot of boat tours heading out of the island as well.