Capital of the province that bears its name, Trang is not a must see in itself, but, with a bit of effort, can be fun.
My suggestion
If you're there during Loi Krathong (the November full moon festival), make sure you enjoy the celebrations at the Buddhist temple. It's beautiful, fun and laid back.
The Khong Chiam region is still largely unaffected by tourism and, for those willing to explore it, offers spectacular scenery and the promise of peaceful days spent well away from the noise and chaos of the urban environment. With its waterfalls, cliffs and rock paintings, Pha Taem is the kind of place you simply never tire of exploring.