mythical island of women
Refers to a legendary island inhabited only by women, appearing in old Japanese tales and folklore.
In old tales, there appears an island called 女護が島 where only women live.
women-only place
Extended modern use for any location or gathering dominated by women, often with a humorous or figurative tone.
This workplace is like an island of women, isn't it?
Irregular okurigana usage; less common but still recognized.
The term combines 女護 (にょご, 'woman') and 島 (しま, 'island'). The exact origin is uncertain, but it appears in classical Japanese literature and folklore as a mythical place.