Avalanche Software has made no secret of the fact that Hogwarts is the part of the game they are most proud of, and it will be possible to explore parts of the gigantic castle that you only partially or never got to see in the movies.
But there's one place you won't get to explore, and that's the Chamber of Secrets. It appears in a leaked artbook (via Reddit), which also reveals that the developers considered it, but ultimately decided to scrap the idea:
"Unfortunately, there were some challenges with this and it was decided not to include it. We certainly wouldn't want the player thinking they could kill a Basilisk that needs to still be there in 1992!"
So the Chamber of Secrets must remain secret, and the justification is undeniably reasonable. The game launches on February 10.