This is very obviously a school.
On the stands, someone was in a middle of a speech:
「 After finishing basic education, you will enter different fields and study skills that are individually suitable to each of you… 」
「 Today, the selection process will begin. Teachers, please head onto the stage for preparation 」
Several teachers who appeared physically strong then carried a heavy metal door from behind onto the stage.
「 Very well, now let me explain the process of the Profession Selection… 」
Standing among the students, Gu Qing Shan carefully listened to their explanation.
It turns out that in this Magic-centric world, children who were around 12 years old would undergo a ceremony called Profession Selection.