A friend living in Turkey recommended I add Pamukkale to my itinerary when I visited Turkey in 2007, and it was a great recommendation. The calcium terraces of Pamukkale are brilliantly white as you approach them from the village below, and I was in awe at the extent of the travertines. Visitors are required to remove shoes when wading up through the series of pools fed from the hot springs at the top of the hill. The water wasn't particularly hot--it was lukewarm at best--but the views from the terraces were spectacular. At the top of the hill was the Greco-Roman spa town of Hierapolis, because who wouldn't want to build an ancient resort in such a beautiful location! The ruins were typical of other Greco-Roman cities, and included a theater, an arcade, temples, and a necropolis. There was also a hot springs pool at the top of the hill, but unfortunately I didn't have enough Turkish lira available at the time to visit the pool.
Logistics: Train or bus to the city of Denizli; minibus from Denizli to the village of Pamukkale.