A natatorium is, strictly speaking, a structurally separate building containing a swimming pool. In Latin, a cella natatoriua was a swimming pool in its own building; thus, the sense was much as now.http://www.psu.edu/dept/nat/ It is usually taken for granted that it will also house locker rooms, and perhaps capacity for allied activities, such as a diving tank, facilities for water polo, and so forth. Many colleges and universities have natatoria.