The name "Clock Tower" has two meanings.
One is, of course, the headquarters of the world of magecraft, the enormous organization.
The second meaning was the school in London - consisting of
Mystile
the Faculty of Fundamentals
, five Major Classrooms and seventy or so Minor Classrooms, it was the highest institute of learning in the world of magi.
To those on the outside, the mass of students just seemed to be attending an old university. And of course, utilizing both mystical and psychological barriers, it was precisely constructed and strictly monitored so that passers-by wouldn't carelessly walk in.
Once you entered the school for real, everything changed.
(...)
In addition to the main school that was the Clock Tower, the remaining eleven Faculties had their own independent college towns scattered throughout the London suburbs, though that was as much due to the geopolitical situation of the Magic Association.