Monastery of Penteli
at 32 seconds on the video:
"The Greek academies of the years after the Fall [of Constantinople] existed as higher education entities of the Church providing invaluable services to the enslaved nation."
TRANSLATION OF THE PLAQUE IN THE ABOVE PHOTO:
The "Secret School" was renovated with the care and toil of the Igoumenos Panosiologiotatos Archimandrite Theokletos Fefes from Kalavryta and the assistance of the Greek government delivered to the Greek Nation for his instruction and opened on May 3, 1971 by His Beatitude Archbishop Ieronymos of Athens and all of Greece, in the presence of representatives of the Ecumenical Orthodox Churches.