I found this glitch while crawling through a sidewalk hole on Hue city when getting to end of the very short tunnel if you turn around you get stuck outside the map YOU do not seem to be able to shoot people outside but i have not tested this
http://steamcommunity.com/sharedfiles/filedetails/?id=1085389576
http://steamcommunity.com/sharedfiles/filedetails/?id=1085389576