Which of the following is classified as a private place?

The principal's office in a school is considered a private place because it is not openly accessible to the general public and is intended for use by specific individuals, such as the school's administration and selected staff or students. This space is typically reserved for confidential discussions, disciplinary actions, or administrative duties, which underscores its nature as a private area within the broader public institution of a school.

In contrast, the other options represent locations that are primarily accessible to the public or used for communal activities. Public parks are open to everyone in the community, city hall serves as a governmental office accessible to citizens for various municipal services, and a school gymnasium is often used for school events and public sports activities, thereby allowing broader access than a principal's office.