The springs have been used as a spa since the second century BC.
The travertine features have their origins in the shifting of a fault in the valley of the Menderes river (between here and Denizli). As the fault shifted, very hot springs with a very high mineral content (notably chalk) arose at this location. Apart from the slightly radioactive minerals, the calcium and hydrogen carbonate react to create calcium carbonate (also known as travertine) and limestone. This is what gives Pamukkale it's whiteness and created the pools.
Closest airport is Denizli - Cardak Airport is 65 km or 1 hour away and there are flights twice daily to Istanbul.
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.)
There are trains to/from Izmir, Ankara and Istanbul.
(The Pamukkale Express has been cancelled in Summer 2008 due to track repairs. No train between Denizli and Istanbul this means!) As on 05 October 2009, the service still suspended.
Bus to Pamukkale/Denizli can be found from almost all the cities of Turkey. Bus services include water, hot drinks and a snack.
There are virtually no bus companies that take you directly to Pamukkale despite what the ticket sellers tell you. The bus will drop you in Denizli and then you have to get on the free minibus to Pamukkale (about 20 km away).
From Denizli bus station, take a dolmuş, a type of cheap communal taxi that usually seats about 10 (but it's possible they'll squeeze in more), from nearby Denizli. Frequent mini-buses serve the village of Pamukkale in a 20 minute ride. It cost 2 YTL per trip.
Even when you're way on the edge of the village, you can reach everything (the village center and the travertine pools) on foot in about ten to fifteen minutes.
Day tours are offered for around 45 Lira (as of January 2010) including English-speaking guide, entrance fee to Hierapolis and the travertines (this alone costs 20 Lira) and buffet lunch. Different companies seem to offer similar tours, ask around. I encountered such tours leaving from (1)the Pamukkale bus company office on the main street opposite the travertines, and (2) the Koray hotel.
The petrified waterfalls/travertine are a UNESCO World Heritage Site. They are a beautiful sight. It cost 20 YTL per entrance. The price is included Hierapolis as well. More pictures and videos of this magnificent view here 
The 12,000 seat Roman theater of Hierapolis should not be missed.
Another lesser known site, but one that holds a considerable significance Biblically is Laodikya, just 10 minutes from Pamukkale on the Denizli road. It's mentioned in the Bible as one of the 7 Churches of the Revelations and even though it hasn't been reconstructed as much as the more famous sites like Ephesus, is a great place to experience the Roman history without the crowds.
Karahyit, the red spring is also 5 minutes from Pamukkale, not as big as the calcium outcrop, but worth a look.
Kaklik caves are like a small version of Pamukkale, but in a cave, underground and are about 30 minutes from Pamukkale.
You can walk down barefooted in the waterfalls from the village on top. The place is crowded when the tour-buses arrive.
You should use slippers. You can not keep shoes dry and some say it is not allowed to use shoes.
Lower part of travatine got more magnificent view compare to top.
You should wear swimming suit. A lot of people bath in the baths here
If neccessary, there is a road up where busses drop of people who only walk down
It gets here very hot
If you stay at one of the small pensions they might give you a tour of the ruins and travertines at night.
It is worth seeing the remains of the ancient city of Aphrodisias. You can rent a van from Denizli to get there. Or the local hotels run tours for approx 25 lira.
Also there are thermal baths at the top of the travertine pools and the ancient city of Hierapolis with a great Amphytheatre.
Of moderate interest might be Denizli it's a bit dull but there's a lively market.
Loadikya is another less visited ruin site only 10 km from Pamukkale on the local dolmus. There are usually few tourists. Peaceful way to spend a day looking at ruins but also the beautiful scenery there as well.
The Pamukkale/Denizli area is famous for its cotton and the homewares. These are becoming sought after world wide (Arnold Schwartzenegger decked out his house in curtains and furnishings specially made in Denizli - so the story goes!) and the best place to go is the town of Buldan, about 30 minutes drive from Pamukkale. Many of the other souvenirs and traditional Turkish wares that you can find in other parts of Turkey are cheaper around Denizli/Pamukkale because they are produced there.
The best and freshest food is to be found in the small family run pensions, but for a great open air restaurant where you can eat 'borek' the Turkish pancakes and gaze across the valley, try Alis on the main highway just before you come into the town.
Mehmets Heaven, on the main street near the Travertines has an excellent view of Pamukkale from his porch out back. Great food and well priced. Super nice owner as well.
Kayas Wine House, Kale Mah. Ataturk Cad. No 3 (centre), ☎ 0090 258 272 2267. Recently started serving food, not only Turkish but also international (Korean, Japanese...) in traditional but trendy surroundings. Located in the centre of town, close to all the major hotels.
Lamuko's Lokanta, Main Street Pamukkale, ☎ 0090 542 390 8175. Japanese and Korean food in the centre of Pamukkale, next to Pamukkale Bus Company office. Delicious!
You should try Turkish national drink called Ayran, which is very healthy. It is an aquired taste though. The wines produced in the Pamukkale area are becoming quite famous and are winning awards for the quality and standard.
Raki!! or lion's milk as it is known, again an acquired taste. Great with fish or any long meal as it is meant to open up your appetite.
There are small family-run pensions at the village south of the travertines. Most have swimming-pools filled with the warm greenish milky water from the travertines. They also offer very delicious Turkish food.
Melrose Allgau Hotel is a nice family-run pansiyon at the eastern end of town with nice rooms for about 32 YTL and upwards. The friendly owners serve cheap but tasty home cooked meals. There's a laundry service and a pool filled with spring water. They also used to allow campers to put up their tents.
Artemis Yoruk Hotel Great location, right in the centre of town and just opposite the bus stop. Great range of rooms, dorm, single, double, triple and family. Price included breakfast. HUGE pool and nice garden, great for relaxing. Traditional Turkish food served all day and night on the rooftop terrace. Owners very helpful and very attentive (fluent English). Lots of tour information including Afrodisias, Laodikya, book exchange, free internet.
Venus Hotel is a comfortable, popular choice with single, double, triple, quad and five person rooms that have been newly renovated and are available for very reasonable prices. There is also wireless internet connection, a swimming pool filled with the famous Pamukkale water and a restaurant where the hotel's guests and other visitors from all around the town get to try traditional home cooked Turkish meals and local wines. They also provide travel services and information and have fluent English speaking staff.
Melrose Residence House Hotel Pamukkale (Hierapolis) is situated on the south west of Turkey's Anatolian peninsula. One of the most familiar images of Turkey is the gleaming-white calcium formations (travertine pools) of Pamukkale in Turkey. In this beautiful region the Melrose Residence House Hotel is located.
Four Seasons Pamukkale Hotel Come to you feel at home, Hotel Dort Mevsim Easily the best place you will stay in Pamukkale. Great value cheap, clean room, nice bathroom, great food and friendly our staff enjoyable!
Ozturk White Hill Hotel One of Pamukkale's best-loved hostels - as it is consistently rated one of the top hostels in the country. We’re a small family-owned and run hostel with a homey atmosphere - the perfect place to relax and enjoy your time in Pamukkale.
Koray Hotel, Fevzi Cakmak Cad. Pamuk Mah. No.29, ☎ 0090 258 2722222, . situated in a quieter area of town, but just five minutes walk to the Pamukkale traventines. Friendly and family-run, with garden bar and restaurant and a large swimming pool. The hotel can organize day tours, express bus tickets, plane tickets, and offers a transfer service.
Kale Hotel, Kale Mah. Ataturk Cad. No.16 (On the main street in the centre of town.), ☎ 0090 258 2722607, . checkin: 00:07; checkout: 00:11. A family-run guesthouse, located in the pleasant village of Pamukkale with a two minute walk to the white terraces (travertines). Roof-top terrace, swimming pool, free wi-fi, Ottoman Corner, restaurant, day trips and excursions. Euro 12. (37.9175536,29.1211402)