The main building is the Mosque of Saints, to its right the The seyyid Ebu’l-Hasan Harakani türbesi (mausoleum). There is an extensive text on the spot, in Turkish. I read the man lived from 963-1033.
Through the left side opening in this "gate" you can see the Citadel tower. A notice indicates: One of the seven large towers surrounding the outer ramparts of Kars Citadel, built in 1153 A by Vizier Firuz Akay upon the edict of Melik Izzeddin of the Saltuks (from the Wikipedia: the Saltukiods were one of the Anatolian beylik of the first period founded after the Battle of Manzikert and centered in Erzurum. Saltukids ruled between 1071 to 1202. The beylik was founded by Emir Saltuk, one of the commanders of the Great Seljuk Alp Arslan. The beylik fought frequently against the Georgian Kingdom for hegemony of Kars region. Center of the beylig, Erzurum, was occupied by Byzantine Empire between 1077–1079 and was besieged by the Georgian King Giorgi III in 1184. It compromised present whole Erzurum and Bayburt provinces also east of Erzincan, most of Kars, north of Ağrı and Muş provinces during its height.)
It has a hexagonal layout and is built of clean-cut basalt stone.