Denizli is an industrial city in the southwestern part of Turkey and the eastern end of the alluvial valley formed by the river Büyük Menderes, where the plain reaches an elevation of about . Denizli is located in the country's Aegean Region.
The city has a population of about 646,278 (2018 census). This is a jump from 389,000 in 2007, due to the merger of 13 municipalities and 10 villages when the area under Denizli Municipality jurisdiction increased almost fivefold and the population around 50 percent. Denizli (Municipality) is the capital city of Denizli Province.
Denizli has seen economic development in the last few decades, mostly due to textile production and exports.
Denizli also attracts visitors to the nearby mineral-coated hillside hot spring of Pamukkale, and with red color thermal water spa hotels Karahayıt, just north of Pamukkale. Recently, Denizli became a major domestic tourism destination due to the various types of thermal waters in Sarayköy, Central/Denizli (where Karahayıt and Pamukkale towns are located), Akköy (Gölemezli), Buldan (Yenicekent), and Çardak districts.
The ancient ruined city of Hierapolis, as well as ruins of the city of Laodicea on the Lycus, the ancient metropolis of Phrygia, are nearby. Also in the vicinity of Honaz, about west of Denizli is, what was, in the 1st century AD, the city of Colossae.
The weather is hot in Denizli in summers, whereas in winters, it may occasionally be very cold with snow on the mountains that surround the city. Some years, snow can be observed in the urban areas. Springs and autumns are rainy, with a mild warm climate.
The word deniz means 'sea, large lake'. No sea or lake can be found near Denizli. However, the original Turkish name for the place was Tonguzlu, pronounced as toŋuzlu or doŋuzlu, later donuzlu (from toŋuz 'wild boar'). Thus Tonguzlu means a 'place where boars dwell'. Because of the phonetical process (t->d, ŋ->n), the name was changed into denizlü or denizli, similar in pronunciation but different in meaning, in order to avoid the connotation 'boar, pig', which is considered offensive in Islam.