Spider Step:
Your physical mastery grants you an impossible stride.
Prerequisites: Acrobatics 6 ranks, Climb 6 ranks, monk level 6th.
Benefit: As a move action, you can move up to half your slow fall distance (maximum 50 feet) across a wall or ceiling or across ropes, branches, or even water or other surfaces that cannot support your weight. You must reach a solid, level surface by the end of your turn or you will fall.
So if there was a bunch of rubble on the ground would you have to spend 2x movement to move over it? Or do you still need feats like Nimble Moves?
Yep it doesn't do anything for difficult terrain.
Throw a rope across it first and walk on that -- or some branches.