Gemiler Island (also called St Nicholas Island) lies just off the coast between Fethiye and Ölüdeniz. The small island is covered with the ruins of Byzantine churches, rock-cut tombs, and a remarkable covered processional way that runs the length of the ridge. The mosaics in the churches are fragmentary but beautiful, and the views from the summit take in the whole coastline.
The island is accessible by boat from the nearby beach at Gemiler, or as part of organised boat trips from Fethiye. Give yourself a couple of hours to explore — the path is rocky and exposed to the sun, so bring water and wear sturdy shoes. The beach on the mainland opposite is a good spot for a swim afterwards.