Check Strength or Dexterity to climb. If a new segment of the climbing path becomes visible, do a second check to progress. Each exploration turn spent studying the climbing route will add half of one attribute bonus (rounded down) to the roll. If the roll fails, the referee should roll a D10 to see what percent is climbed before the fall.
Designer's Note: Climbing isn't the easiest thing to make a ruling on, and this system is simple with interesting results.