ward residents' hall; municipal community centre
A public facility in a city ward (区) used for local events, meetings, and community activities. Similar to a community centre but specifically tied to a ward administration.
A yoga class is being held at the ward residents' hall.
I reserved a meeting room at the municipal community centre.
区役所 is the ward office (administrative building), while 区民館 is a separate community hall for residents' activities.
Compound of 区 (ward) + 民 (residents) + 館 (hall/building). A straightforward modern coinage for a ward community facility.