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locked room
secret room
密室で起きた事件は謎が多い。
The incident that occurred in the locked room is full of mysteries.
この小説の密室トリックは見事だった。
The locked room trick in this novel was brilliant.
密室の中で長時間過ごすのは息苦しい。
Spending a long time in a sealed room feels suffocating.