A Reddit-user has found out that the NPCs in Fallout 4’s Diamond City (the “capital” of Fallout 4’s world) celebrate Holidays like Halloween and Christmas.
Around Halloween, the guards in the city talk about the festival and when it’s Christmas, they even hang up some lights and place (fake) Christmas trees! It’s impressive a tradition will have survived for so long. I’m actually really wondering what their Christmas-story is, since Baseball also gets remembered as a sport where everyone would hit each other with a bat, until one team is murdered (the other wins).
The city will be in Holiday-mode when the holiday is happening in the game, not the date of your PC or console. You can find the in-game date in the bottom-left corner of your Pip-boy when looking at the map.
Check out a video of Christmas in Diamond City below.