監獄

1. Origins, structure, and basic meaning

• Structure: 監獄(かんごく) means a prison, a facility where people are confined.
• Basic usage: It is used for prisons in films or buildings formerly used as prisons.

2. Common pitfalls and similar expressions

• A building's former use
  • かつて監獄だった建物 means a building that was once a prison. だった marks its previous state.
• Its present role
  • 資料館として means as a museum, indicating the role in which the building is now open to the public.