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've made it into Kings Watch in a similar manner. But a ton of Level 20's and an Ultra Captain spawn there making it hard to traverse. Here's a link to my video: http://www.youtube.com/watch?v=Ajz9l1aHCj0&list=PLnjoAR4NkCy-MmS-t-rta629JDb36ch0j