Zinciriye Medresesi
Free
on the hill towards the citadel; look for the sign on the main street
A madrasah Islamic school built by the Artuqids, rulers of the area then, in 1385. Rooms surrounding the central courtyard have some beautiful wall and ceiling decorations, having similarities with Seljuq art of central Turkey. Definitely a must-see while in Mardin.
Citadel
on the hill overlooking the old city
While the citadel itself is located inside military zone and thus is closed for visitors, ascent the alleys of the old city to get to as near as possible to have the fascinating view of the Mesopotamian plains lying below. However, never ever try to cross the heavily barbed wire, as it equals to suicide according to locals.
Church of Forties
in a side alley; look for the small sign on the main street
A Syriac Orthodox church dating back to 10th century.
All sights of Mardin are located in old city.