On this page of our spoiler-free guide to The Last of Us 2 you can find a list of all secrets available in The Constance 2425 level. It's one of the missions that is a part of the final chapter of the story campaign - Santa Barbara. In this stage you play as Abby - you can only find one secret in this level.
List of collectibles available in Constance 2425 level
Constance 2425 level has only one secret:
As you travel down the main (overgrown) street you will notice a house on the left. The infected are wandering around the building. Defeat the monsters and look inside. Note - If you haven't already started the alarm, there may also be monsters inside the building.
You can find the note in the bathroom.