The Madrasa-i Kuhna, or Old Madrasa, sits opposite the fortress gate and is the most substantial surviving building on the site. It is a low, square structure with an arched portal and a courtyard ringed by student cells. The brickwork is plain by Bukharan standards but the proportions are dignified.
Inside, the cells have been turned into a small museum of Hisar history, with displays on local archaeology, the emirate period, and the surrounding villages. Allow twenty minutes to walk around. The acoustics under the central dome are worth a brief test.