This is a video showing how to get into a secret room in Winter Contingency. Its a very large room and contains some pictures and generators. there is also sort of a second floor in the room as well.
I hope you enjoy the vid :)
[url]http://www.youtube.com/watch?v=3Q8EzFlBzFQ[/url]
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Not really a secret room. You spawn in there for Firefight. The door is closed, that's all.