Pilgrims and travellers who want to go the the Holy Mountain need a special passport; the Diamoniterion. This document can be obtained in the pilgrims bureau in Ouranopolis after you have made your official reservation in advance ofcourse. Ouranopolis is the town where most of the ferries leave for Athos. 
This is the entrance to the office. Inside it is pretty crowded and you have to wait a while. Passports have to de checked, forms have to be filled in and printed.
On one of the walls there is a poster showing the dresscode. In the pilgrims bureau you are explictly reminded of this: no piercings, no sandals, no shorts, no topless, no bare upperarms etc. Here is how it´s shown; the do´s and don´t on Athos:
Pilgrims Jaap and Herman were pretty proud when they finally received the well-desired document in late september 2009. The Diamoniterion is the first step to the Holy Mountain.
Bas Kamps
Bonjour !
Des amis lecteurs français (http://www.moinillon.net/post/2011/01/15/YES-NO#comments)sont intrigués par l’interdiction sur la photo au milieu, en bas, où l’on voit un homme en sandales.
Savez-vous de quoi il s’agit ?
Ces sont des sandales avec des chaussettes. C’est acceptable. Mais il ne faut pas porter des sandales sans chaussettes.
English translation;
Hello! French readers and friends: (www.moinillon.net/post/2011/01/15/YES-NO # comments) are intrigued by the ban on the photo in the middle, bottom, where we see a man in sandals. Do you know what that is?
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These are sandals with socks. That is acceptable. But do not wear sandals without socks.
Posted by: Bas Kamps, 19/01/2011