On Downfall go to where this kid is on the map. Then go up against the wall and look down, then start hopping up and down, eventually you’ll go under the map. And to get back on the map get in a tank then get out.

A Call of Duty: World at War glitch for your exploiting pleasure.

This is and alternative way to get under, outside and back in castle. Basically go were i am on the map, and jump toward the wall, if you do it right you’ll go right through.