The island is located approximately 9 km to the south of Fethiye and it is 1000m long by 400m wide. The south slope of the island is very steep where the northern slope shows a slight incline.
Gemiler or St. Nicholas Island situated at the Ölüdeniz lagoon area was known as Smybola in medieval period. It became a prominent religious center especially in the 5th century B.C.
There are various narratives about the name of the island. According to one of them encountered in a medieval maritime book is; the church at the highest point of the island was dedicated in the name of St. Nicholas. However, it is not yet verified whether this Nicholas is the same as Saint Nicholas of Demre (Myra), more popularly known as Santa Claus. A certain Nicholas lived on this island, but there is not detailed information about his identity yet.
In 1990, a surface survey has been carried out by a Japanese team. After this, archaeological excavations conducted by Directorate of Fethiye Museum together with Japan Osaka University in between 1995 - 2003. Besides eleven basilica type churches also many chapels, houses, storages, graves, and cisterns were found during the surveys carried out on and around Gemile Island and Karacaören Island. Religious structures were built of mostly local stones partly hewn stones and rarely brick. Churches on Gemile Island were decorated with fresco walls and mosaic floors however the mosaic floors were mostly damaged. There is a 160 meters long and 2.5 meters wide vaulted road between second church and the third church, which are situated on the east and the west edges of the island respectively.
It is easy to distinguish the religious buildings situated at the top of the hill from the civilian and commercial buildings at the bottom with the help of a wall separating them. This wall extends through east-west direction in the northern slope of the island. This shows that the top of the island was a sacred site.
There is a chimney at Karacaören Island assumed to be used as a communication device which produced smoke in cases of possible enemy attacks to warn people of both Gemile Island and Kayaköy village.
Gemile Bay, Ölüdeniz, Fethiye peninsula, Žövalye Island and 12 islands are situated in the same gulf which Gemile Island is at the center. There are many church and chapel ruins spread all over this gulf which gives the impression that the area was busy with religious activities in that period.
There used to be settlements at Gemile Island and its surroundings between 5th-13th centuries B.C. The excess of religious buildings can be explained as a result of an increase of pilgrimage through sea, from front Asia to Aegean and Mediterranean coasts between 5th-7th centuries B.C. Also this fact reveals the relationship between old ages, Byzantine and near East, Europe in terms of maritime trade.
There are houses of people living and working at the outside of the religious buildings. Since it is a rocky terrain, the foundations of the churches and the houses are carved into the rocks. The ruins continue within the sea along the shore.