Ephesus is the ancient city in Turkey, a World Heritage Site, that features the Library of Celsus.
Located near modern Selçuk in western Turkey, Ephesus grew into one of the major cities of the ancient Mediterranean. Its location shifted over time as sediment gradually filled the nearby Kaystros estuary and pushed the coastline westward. Under Roman rule, Ephesus became the capital of the province of Asia and a major port, commercial centre, and pilgrimage destination.
The Library of Celsus was built in the early second century CE in honour of Tiberius Julius Celsus Polemaeanus, a Roman governor. Its monumental façade, with columns, statues, and multiple levels, is one of the best-known surviving features of the archaeological site. The city also contains the Great Theatre, the Temple of Hadrian, terrace houses, and remains associated with the Temple of Artemis.
Ephesus was inscribed on the UNESCO World Heritage List in 2015. Aphrodisias, Pergamon, and Troy are also important ancient sites in Turkey, but none is the canonical answer to a question specifically identifying the Library of Celsus.