Heading towards the Valkyrie at the end of the map, just after the drop-down and before the bridge, going left and jumping on the spikes/gargoyles hanging from the walls allows to leave the map. Jumping from this place is a long fall resulting in death.
Steps to Reproduce:
Play Enclavum Barross and just go left just before the end of the map. Jump along the wall 'till there are two little drops, and you’re out of the map on tangible ground.
Still a pretty sight though!
Mission Name (If Applicable):