An anacopia or defensive structure.
The story can be found on the Internet, and I'll tell you about this place:
You can get to the foot by taxi or by car by paying 200-300 rubles for parking. And after paying the eco fee of 300 rubles per person, we go on a trip.
The route is on a light and even adults can master it, it takes 40 + minutes to get to the top. Be sure to climb the eastern tower, it was restored not so long ago and from there you can enjoy a stunning view of the entire new Athos, the monastery station and even Sukhum.