Hierapolis and Pammukale are good places to visit in Turkey. Unfortunately they have begun to suffer from a bit of over-development. This is especially true of the travertine pools. They are now mostly dry and you can no longer bathe in them. Some of them are even artificial now! The ruined city, on the other hand, is pleasant. There are usually not big crowds and even if there are, you can escape them easily enough. The thermal pool at the top of the travertines is pricey (18 lira a pop), but worth it if it's not too crowded.