I'm looking for a period piece movie where there's a gazebo or summer house in a lake and the house has steps into the lake and when the lake is frosen in the winter they can walk to this building. It seems like there's an affair of some kind involving a nanny or sister?

I'm looking for a movie where there's a gazebo or summerhouse in the lake and the steps of the house go into the water. When the lake is frozen they can walk to this building. It was a period piece and it seems like there's an affair between the man and a nanny or maid or sister or something.