they were only allowed to leave the scriptorium once a week , and even then they were forbidden to step outside the castles walls ; their fine robes were tailored and their sumptuous meals prepared by others , regardless of their personal taste ; and as for the scriptorium itself , it was a gloomy , dank tower at the very edge of the castle , its only view and that from its top , for the scribes chambers were windowless a grey expanse of sea and sky stretching as far as the foggy bank that hovered above the drowning isles .