Hint: Its underneath the map. http://www.bungie.net/Online/Halo3UserContentDetails.aspx?h3fileid=58739411
*Sigh*.. yeah.. I guess everyone knows about this? It happened to me so randomly and it was the first and only time it has happened to me so far..
It's not that hard to get out of the map either. Do you know how to use the turret glitch? That's exactly how you get out.
No... actually this happened to me in ranked Team Slayer (believe it or not). We were playing duals in Boundless and someone killed me in the basement by where the shotty respaws and I fell through the map. That spartan diving is actually me dead falling through the map...