I found the secret room quite easily but I had trouble getting into it. In the end I made a mind map of where the room is and how it could possible be accessed. The clue that it is behind a statue of Benjamin Holger didn’t really help me because firstly I didn’t know who he was and now that I do the statues are all over the place. This guide shows you where the secret room is:
One of the ways you can enter the area is through the Kennels. If you know where that is the entrance to the secret room is opposite the exit of the Kennels. If you don’t know where that is check the video at the end of this post, it will show you how to get there from the main entrance.
All you have to do is push the eye of the statue: