seven wonders (of a particular area)
Refers to a set of seven remarkable or mysterious things in a specific region, school, or context. Often used in phrases like 世界の七不思議 (Seven Wonders of the World) or 学校の七不思議 (seven mysteries of a school).
See also: 世界の七不思議
I'm researching the Seven Wonders of the World.
Apparently this school has seven mysteries.
total mystery; enigma; conundrum
Jocular or humorous use; describes something completely baffling or inexplicable, as if it were one of the seven wonders. Often used in phrases like 七不思議だ or 七不思議の一つ.
How he passed that test is a total mystery.
The way this machine works is one of life's great enigmas.