Hi Geoff,
If you want to go the north region, i recommend to you Karadeniz of course. Rize (Ayder, Çamlıhemşin, Fırtına Deresi, Zil Kale) if you like they have a very nice rafting zones , Trabzon (Uzungöl, Sümela), highlands (Dolit, Olovit in Erzurum and Karadeniz Border), Artvin. And taste the delicious Karadeniz Foods (Hamsili pilav, mısır ekmeği, kuymak, all kind of fishes). As you know the region is also famouse with it's tea and nuts.