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Photo: Yerevantsi, CC BY-SA 4.0 via Wikimedia Commons
Built as an Armenian church circa 930 AD, it was probably abandoned in 1046 when the Seljuks took over - they may have used it as a mosque. It was certainly a mosque after the Ottomans captured the city in 1579 and made it part of the Evliya complex. The Russians reverted it to an Orthodox church in 1877, but when they withdrew it was back-and-forth between mosque and church as the frontier shifted. In the 1960s it housed the city museum, until that moved edge-of-town. It's again been a mosque since 1993.
The Cathedral of Kars, also known as the Holy Apostles Church is a former Armenian Apostolic church in Kars, eastern Turkey. Built in the mid-10th century by the Armenian Bagratid King Abas I, it was converted into a mosque in 1579. In the 19th and early 20th century it was converted into a Russian Orthodox and later Armenian cathedral. In 1993 it was again converted into a mosque and is called Kümbet Mosque. It currently comprises part of a larger Islamic complex that includes the Evliya Mosque, the biggest mosque in Kars.
© OpenStreetMap contributors
The castle or citadel was built from 1153: it's been destroyed on several occasions but restored. Approach up the cobbled track from the south. Within is a small mosque, and the reconstructed tomb of Kahraman Celal Baba, a mythical 13th century hero against the Mongol invasion. There's not much else within but you get a view of the city. The mausoleum at the foot of castle hill by Taş Köprü is for two other fallen defenders.
Kafkas Cephesi Harp Tarihi Müzesi
This bastion was built in 1803 to protect the city from the south, which it failed to do: in 1828 the Russians raided it and slaughtered the entire garrison. It's now a branch of Kars Museum exhibiting the Caucasus conflict, signage is only in Turkish.