Our taxibus that would take us to Karyes suddenly stopped for a sanitary stop by the side of the road. We took the opportunity to look around. We were close to the arsanas of Karakallou. We saw this impressive mediaeval tower just in front of us.
I tried to find more and older pictures of this tower but I did not succeed, except for this one. This is a still from a film dedicated to the celebration of 1000 years of the Holy Mountain (the French Pathé millennium film is shot in 1963). See here. The still is after 18 seconds. It seems that there is hardly any material about this castle in the English language.
There is a wonderful artist impression of Karakallou arsanas made by Dominique Papety. We showed the art of Papety (1815-1849) before. He went to Athos twice and made many pictures. He died at a young age from cholera.
This is the perspective Google Earth gives of the situation. The interior of the tower and the adjacent walled castle seems to be filled by nature. So nature will take over if the roof is not restored.