Kayseri Castle is the dramatic centrepiece of the old city, a substantial Seljuk fortress of black basalt that has stood in its current form since the twelfth century, though its origins go back to Roman times. The walls rise in a rough rectangle around the city centre and still contain 18 of their original towers. The black stone gives the castle an unusual severity compared with the pale limestone buildings of the bazaar quarter surrounding it.
The castle was extensively restored under the Seljuks and later the Ottomans. Today the walls form the perimeter of the city's central district, and the interior has been converted to house the Kayseri Archaeology Museum, which since 2019 occupies purpose-built exhibition halls within the castle grounds. Walking around the outside of the walls and through the main gate is free and gives a strong sense of the castle's scale.
The surrounding area — Cumhuriyet Square — is the social heart of the city, with tea houses and pastırma shops occupying the streets between the castle and the covered bazaar.