The shattered apse is all that remains of what was once a 7th-century Armenian cathedral, rebuilt by Georgians in the 9th century and used for royal weddings, coronations and burials. The ruin, standing on a lonely hillock, is briefly visible as you drive past on the glorious D060 Oltu–Ardahan road: look north some 11km east of Yolboyu.
The site itself is still strewn with huge chunks of tumbled masonry, resulting from earthquakes and the cathedral's bombardment during the Russo-Turkish War of 1877–78. To get there, drive to Penek village (14.3km east of Yolboyu then double back 2km to the west). The ruined cathedral comes into view from the top of a rise just past Penek graveyard. A dirt road branches off left to the site 300m later (don't brave this with an ordinary car in wet weather). Climb the hillock for a panorama of bright green grasslands backed by colourful badlands.