This rope, found dangling over a yawning gulf, appears to have been used to swing from one side of the chasm to the other – the length is correct, and it doesn’t give when yanked on from the near edge. However, that’s because of the angle at which it is being pulled. When the force is directed straight down, a spring-loaded reel suddenly pays out another two metres.
When the rope spools out, characters can make a DC 18 Reflex save to respond in time, and if successful can make a DC 20 Climb check to scramble up the rope high enough to clear the lip of the cleft. If they succeed, they can roll onto the far ledge; if they fail by less than 5, they hit the lip and take 1d6 non-lethal damage, but can grab on and pull themselves up (though depending on their Strength and current load, you may require Strength checks for this).
If they fail their Reflex save, they slam into the side of the chasm, dealing 4d6 non-lethal damage and (assuming the victim is still conscious) forcing a Fortitude save equal to the damage dealt to hold onto the rope.
If they let go, the rope spools back in to its original length, and they find out what’s at the bottom of the cleft (taking falling damage as appropriate); if they hold on, they can climb up the rope to a point where they will no longer hit the opposite wall, but have lost considerable momentum and will need to spend 3 rounds swinging on the rope to build up their speed enough to make the far side.