Corrected entry: The sealed off room in the L'American hotel is a fantasy. For one, a maid or the owners should spot that a room is missing from their own hotel. Secondly, we know that Mr. White visited frequently, and as recently as the events in Casino Royale as evidenced by Vesper Lynd's interrogation tape. Whilst it's conceivable he was able to secure the same room every year, that he was able to replaster and repaint the wall as well stretches belief.
GalahadFairlight
12th Nov 2015
Correction: Mr. White could have bribed the hotel staff to keep the room a secret. They probably redid the wall too.