in the walls and gradually ascends to the top. A rope can then be rigged to the bottom, allowing following cavers to pass the obstacle. Some avens have been tackled by lifting ropes or ladders using long poles (Maypoling). Narrow avens can be climbed by pushing against opposite walls (chimneying). See also Multi-pitch climbing Grade (climbing) References External links The world's deepest pitches, by Bob Gulden Caves with the deepest drop, by Jochen Duckeck Climbing Caving