Denizli is the commercial and transportation hub of Aegean Turkey. It is nesteled against the hillside at the southern side of the Buyuk menderes river plane. It's a busy place partly because of nearby Pamukkale and its travertine pools but mainly because it's the main commercial hub for the agricultural produce coming from the region. It's also the place where you probably need to go if you're in need of cash.
Don't let it's looks deceive you when you arrive at the Otogar once you proceed beyond the main thorougfare and it's dreary concrete facades which are repeated throughout the city, you find there's a lively market and all sorts of eateries. Since tourists don't really come here, you probably won't be harassed.
There are busses here (directly or indirectly) to and from Nevsehir (for Goreme), Istanbul, Fethiye and Selcuk (for Ephesus). Actually, as a whole, Turkey offers a very well connected bus system. You can reach almost every cities of Turkey from Denizli. The most notable ones are Adana, İzmir,İstanbul,Diyarbakır, Ankara and so on.
You can take a so called "dolmus" (minibus) from here to Pamukkale they run approximately twice an hour.
There are trains to/from Izmir, Ankara and Istanbul. However, unfortunately, the train connections of Turkey are as good as its European counterparts. There is still a construction work on the railroad that connects Denizli to Izmir and Istanbul so always try to avoid using trains.
Trains between Istanbul and Denizli seem to be out of order. Verify with seat61.com
Closest airport is Denizli - Cardak Airport. The national carrier Turkish Airlines provide two daily services from Istanbul Ataturk Airport. (Check Turkish Airlines Official Website THY )
Izmir Adnan Menderes Airport is another alternative to the area. Pamukkale is 252 km from the airport, a drive of about 4 hours (4-1/2 to 5 hours by bus)or 6-7 hours by train. (Check TCDD  for train schedule).
Bus to Pamukkale/Denizli can be found from almost all the cities of Turkey. Turkish Buses are reliable, almost always on time. When you consider to buy a ticket always try to use the well-known companies. Usually they have bigger signs in the so called "Otogar"(Bus Terminal)s. Also, always check your departure time and gate as well as the destination. The agent most probably will not know any word in English so you may need to use Body Language instead.
Denizli is not a very big city. You won't need to use the transportation system very often. Minibuses and buses provide service. There is either metro nor trams running. Just rely on your foot as the center of the city is so small. If want to go to outskirts of the city you can take buses. Every bus has a sign on it stating where it goes and terminates. You can try to ask the driver as well.
As not being a very popular tourist destination Denizli do not have tons of stuff to offer. However, there are very beautiful parks in the city. They are called as "İncilipınar Parkı" and "Çamlık". You can go there to take some fresh air. There is one very famous museum which was the house used by Mustafa Kemal Atatürk - the founder of modern Turkis Republic - when he visited Denizli. Also, there is a very important historical site in Pamukkale on the ancient site of Hieropolis. In that historical site, you can find a well preserved ancient theater and graveyards. Hieropolis Mesuem and antic site is well worth seeing.
Denizli is a very well-known textile city in Turkey. It may offer you a wide-variety of textile products. Also, one can find some hand-made clothes and so on. The biggest place for buying traditional handmade clothes is "Babadağlılar İşhanı" located in the heart of the city. Moreover, huge shopping malls such as "Teraspark" and "Forum Çamlık" are good options for famous world-wide-known stores.
You can find some different choices in Denizli to eat. The very first one of these is "Denizli Kebabı" The best denizli kebabi is at enver kebabci that is located at bayramyeri . You can taste it in "Bayramyeri" district. It is also known as "Tandır" in some parts of Turkey. Denizli Kebabı can be consumed best in the mid-day. Also, another option would be "Kaşarlı Alabalık". A kind of meal made from fish and cheese in a very special oven. You should also try the toasts of "Karadam" which is located in the city centre "Çınar". The "Dörtlü" is something that you should not miss.
The places to stay in the city centre are not the only choices. Pamukkale and especially Karahayıt offers some better places to stay at affordable prices. In the hotels of Karahayıt you can have a good service including special messages and thermal SPA. Be aware that in some hotels around the "Otogar" you may face with some illegal activities such as prostution.