In the first blue room you enter, there is 3 Nazis and a fireplace. Shoot the picture over the fireplace... well, ok, shoot the Nazis first, then the pic... and a swastika shows. Shoot that too. A door opens under the great staircase in the next room. The door will shut again, but there is plenty of time to reach it.

In the library, there is a open fireplace with a poker and some other tools in a rack. Pull on the poker - then the fireplace slides aside and reveal a secret room.