From what I experienced, you need to have captured all four heroes in the story line and then visit the Forest several times after. A scene will randomly trigger for it.
I spent days just trying to capture or tease the foxes who were snagged by the woods, but only after I got the 4th hero did it happen eventually.
Also, don't know if it matters, but I had upgraded everything in the house, so stove, work bench, milk shed.