Its in the bashee fighting room. just watch the video
http://xboxdvr.com/gamer/EIectr0n/video/12788945
When you reach the black round thing you need to go exactly where i went (there is a hole in the invisible wall there), Then boost out for about 10seconds, then turn around and fly towards the highest map part you can see (it should be a white box, or black, or both, the black box/room can only sometimes be seen), if you dont you will likly hit a kill box. It will take you to the external of the previous room (the one with the skull). I havn’t seen where else i can go. Go explore my friends.