The black school

Some brave wizards of Europe, it was said, learned forbidden knowledge in a school presumed to be in Spain - a cavern reached by winding staircases leading far into the earth and sealed from the sunlight by iron doors.

Except for their own murmurings, the scholars had a silent schooling. They saw no schoolmaster and heard no responses to their questions. The answers they asked for each night appeared in the morning as letters that glowed and faded on the pages of their books or shone from the cavern walls.

No servants brought the wizards sustenance. Instead, a shaggy hand thrust out from the walls the food and drink they required. No fee was asked save one - that the last man to leave each class give his body and soul to the schoolmaster, whose name was Satan.