Here are my top five recommendations for daytrips in winter. All are in An Hour From Paris except for Malmaison, which is in Half An Hour From Paris.
Conflans Ste Honorine
Watch or join the dancers at the Guinguette Auvergnate riverside restaurant. Optional short riverside walk to the station at Choisy-le-Roi.
Visit the Villa Savoye built by Le Corbusier in 1929. Optional short riverside walk to the station at Villennes sur Seine.