Aydin (Güzelhisar), ancient Greek Tralles, is a city in and the seat of Aydin Province in Turkey's Aegean Region. The city is located at the heart of the lower valley of Büyük Menderes River (ancient Meander River) at a commanding position for the region extending from the uplands of the valley down to the seacoast. Its population was 207,554 in 2014. Aydin city is located along a region which was famous for its fertility and productivity since ancient times. Figs remain the province's best-known crop, although other agricultural products are also grown intensively and the city has some light industry.

At the crossroads of a busy transport network of several types, a six-lane motorway connects Aydin to Izmir, Turkey's second port, in less than an hour, and in still less time to the international Adnan Menderes Airport, located along the road between the two cities. A smaller airport, namely Aydin Airport, is located a few kilometers in the South-East of Aydin. The region of Aydin also pioneered the introduction of railways into Turkey in the 19th century and still has the densest railroad network.

The province of Aydin is also where a number of internationally known historic sites and centers of tourism are concentrated.

The weather is hot in summer, and warm all year round.

Places of interest include:

• The Ottoman period mosques of Ramazan Pasa, Süleyman Pasa and Cihanoglu
• The Byzantine tower and fortifications above the town
• Roman era ruins (of Tralles) including a gymnasium and a theatre
• The statue of Yörük Ali Efe in the town, which was pulled down and remade after public protests that the original statue showed the efe without a moustache.
• Aydin Museum - archaeology, coinage and ethnographic collection
• Recreational resorts Pinarbasi and Aytepe, which are connected by the Aydin Pinarbasi-Aytepe Gondola.