Edit: Here is a video walk-through of the bunker!
https://www.youtube.com/watch?v=QFynhHBPzm4&feature=youtu.be
http://i.imgur.com/i7KJeJG.jpg
http://i.imgur.com/jOtxWlb.jpg
Here is a tutorial on how to do it.
http://www.reddit.com/r/DestinyTheGame/comments/2b80fh/hidden_area_glitch_seraphim_vault/
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I find this name very interesting. "Seraphim" refers to high angels, sometimes the caretakers of God's chair or simply major angels in the angelic pantheon. I wonder what might be hidden in there, maybe preserved alien artifacts of the Traveler or of other life forms that came before the Collapse. Yet I do think it's likely that Rasputin is also hidden in that bunker.