Gazi Kosk is a historic mansion set below Diyarbakir's old city, near the green edge of the Tigris valley. It is associated with Mustafa Kemal Ataturk's time in the city, but the broader appeal is the combination of black-stone architecture, gardens, and views back toward the walls.
It is a good stop after walking the ramparts and Hevsel Gardens, especially if you want to see how the city steps down toward the river. The site is more relaxed than the dense old-city streets, and it helps connect Diyarbakir's political memory with its landscape.