As for Denizli overall I have to say it is nice, but not really a place to see much -- it's just a regular little town. It is very close to Pamukkale and Hierapolis, etc.
Pamukkale is okay, but spare the trip to the "red water source" - it is nothing to speak of, rather disappointing. With a little time try White water Rafting! The guy with the paraglider on top of the terraces runs excellent trips to a place near Denizli. Great fun!
I am an English person living in Denizli -- there is plenty to do and see. It depends what you're interested in and when was the last time you were here, because a lot has changed.
We had a great three days in Pamukkale. A great day trip is Aphrodisias, it has a great stadium and museum.
We highly recommend the white water rafting -- it was the best day we had in Pamukkale.
Ozgur Hotel & Hostel in Pamukkale This is a very good hotel.
Meltem Hostel in Pamukkale This is a great place with friendly and helpful staff. I enjoyed the mineral pool and the home-cooked Turkish foods. Thanks for a great time, guys!
Meltem Hostel in Pamukkale This is a very relaxing and friendly family place. I really enjoyed the food and the service. Thanks for a great stay!
Ozgur Hotel & Hostel in Pamukkale This hostel is clean and friendly, close to the sights, and the bus stops right outside the place. I wish I could have stayed longer.
Ozgur Hotel & Hostel in Pamukkale The food here is exquisite! Without a doubt, it's the best in Turkey! This place also has clean rooms, friendly staff, a refreshing pool, and a great location. What more can you ask for?
Meltem Hostel in Pamukkale It was a great place to stay and relax. The staff were very helpful, and the food was fantastic.
Ozgur Hotel & Hostel in Pamukkale I love this place.
Meltem Hostel in Pamukkale Prices changed daily. A little bit of consistency would have been good.
Meltem Hostel in Pamukkale It's true that Pamukkale is a great place to stay and relax, but I found the staff was a little too "friendly" to the lone girl traveller. Maybe if you're in a group it's okay. I'm just tired of fending off advances. But otherwise, okay.
Meltem Guesthouse & Backpackers Inn in Pamukkale There are many good things about this hostel -- it is as cheap as they come, the rooms and pool are nice, good location, and the hotel manager was quite friendly. On the negative side, the hostel appears to have gone downhill since its high recommendation in Let's Go 2003. The only guests we saw when we stayed there in late June 2006 were a number of women of questionable profession. And if you stay there, don't order the "bottled water" at their restuarant as they'll serve you tap water instead (which will make you sick).
Ozgur Hotel & Hostel in Pamukkale I am from Hong Kong and this hotel said staff would meet me in Denizli after my travel from Antalia. They promised they would meet me and they did not. The night tour was good but at night in the hotel there are watchmen. The hotel is far away from terraces and their staff is much too familiar with the tourists, with bad and sexy jokes.