Which film is Marilyn dress blown up above her waist by a passing train below her?

You're thinking of the iconic scene from the 1955 film "The Seven Year Itch" starring Marilyn Monroe.

The scene takes place on a hot summer day in New York City, where Monroe's character is standing over a subway grate, trying to stay cool. As a train passes underneath, the wind from the train blows her white dress up, revealing her legs.