Just south of Denizli, the ancient city of Laodicea is one of the largest and most active archaeological sites in Turkey today. It was a wealthy Roman commercial city, famous in antiquity for its black wool, its banking, and its medical school. Earthquakes wrecked it in the third and seventh centuries and it was eventually abandoned, but the ruins cover a vast plateau and excavation has been continuous since 2003 under the Turkish archaeologist Celal Şimşek.
Highlights include two well-preserved theatres, a stadium, a vast colonnaded main street, two complete agoras, and the recently uncovered Church of Laodicea — one of the seven churches of Revelation, with its layout, baptistry, and decorated floor mosaic visible under a protective roof.
The site is right next to Denizli (around 10 km north of the centre) and easily combined with Pamukkale, but most coach tours skip it, so you can have parts of it largely to yourself.