Diyarbakır is defined by its walls — a nearly continuous 6km circuit of black basalt built by the Romans and extended by successive rulers over two millennia. Walk stretches of the top for views over the old city rooftops, the Tigris valley below, and the flat steppe stretching south toward Syria. The walls were inscribed as a UNESCO World Heritage Site in 2015, together with the hevsel bahçeleri — seven hundred hectares of market gardens in the flood plain below the walls, cultivated since the Neolithic.
Inside the walls, the old city (Sur) is dense with mosques, hans, and old stone houses built from the same black basalt as the walls themselves. Diyarbakır is the largest Kurdish-majority city in Turkey and the de facto cultural capital of the Kurdish southeast. The atmosphere is distinct from western Turkey: the food is different, the language shifts between Turkish and Kurmanji, and the street life has its own rhythm. The city has been through difficult periods in recent decades, and parts of Sur were damaged during fighting in 2015–16, but restoration work is ongoing and the major monuments are open and well maintained.
The Armenian, Syriac, and Kurdish layers of the city's past are all visible in the architecture. St Giragos Armenian Church, one of the largest Armenian churches in the Middle East, was heavily damaged and has been partially restored. Syriac Orthodox St Mary's Cathedral still holds regular services. These places are open to respectful visitors and repay a quiet hour.
Two full days does the city justice. Give the walls a morning, the mosques and hans an afternoon, and save your second day for the Hevsel Gardens and the Tigris bridges. The city also makes a useful base for the surrounding region — Mardin is 95km south, Hasankeyf 95km east.
For practical orientation, collect a map from the tourism office in the Kültür Sarayı building near the old city centre before you set off into the lanes of Sur.