Okay, quick question. I've got a hall. I've got a 5 ft. tall barricade. I've got nasty undead manning this barricade. Say one of my PCs wants to run down the hall and climb up this barricade. If their is a creature on the other side of the barricade that threatens the area the PC will be climbing through, does it get an attack of opportunity? Or does the PC, climbing as a move action, get through with no problem?