Des irae secret place

[Ohn0es]

How do I get in here?

http://i.imgur.com/Afzpc.jpg

[Dr_Mr_Ed]

Shoot at it. The top section will open.

[FlashSoul]

To be more precise, shoot at the kind of button "in front" of the gate, on the floor.

[Lam]

It's a good idea to shoot it few seconds before the quad, to have quick escape route in case you're attacked from LG room. But don't use it if NG area isn't secure :)