It’s an underground path for people to cross the streets... there is a movie called “irreversible” (by Gaspar Noe) with a notorious “passage souterrain” scene with Monica Bellucci 😏😏

Thank you, but doesn,t it have an idiomatic meaning too?

Reverso offers: ( https://context.reverso.net/traduzione/francese-inglese/un+passage+souterrain ) an underpass an underground passage an underground passageway an underground walkway pedestrian underpass a subterranean passage