Pamukkale, 18 km (11 miles) north of Denizli (map), is Turkey's foremost mineral-bath spa because of its natural beauty: hot calcium-laden waters spring from the earth and cascade over a cliff. As they cool they form dramatic travertines of hard, brilliantly white calcium that form pools.
Named the Cotton Fortress (pah-MOOK-kah-leh) in Turkish, it has been a spa since the Romans built the spa city of Hierapolis around a sacred warm-water spring. The Antique Pool is still there, littered with marble columns from the Roman Temple of Apollo. You can swim in it for a fee.