開あかずの間ま

expression, noun

room that is never opened; locked room; forbidden room

Refers to a room that is kept closed and inaccessible, often with a sense of mystery or taboo. Commonly appears in stories about old mansions or secret chambers.

• 古ふるい屋や敷しきには開あかずの間まがあるという噂うわさだ。

  There's a rumor that the old mansion has a room that is never opened.

• その扉とびらの先さきは開あかずの間まになっている。

  Beyond that door is a locked room.