Rise of the Runelords
Thistletop C9 Rope Bridge
"A rope bridge spans the gulf between the cliff and a roundish, flat-topped island sixty-some feet to the north. Thick patches of nettles and briars grow here and there atop the island, but its most impressive feature is a wooden one-story stockade. Two thirty-foot-tall watchtowers guard the stockade's southern facade. The rope bridge itself is made of hairy rope and thick wooden planks; the whole thing creaks and sways in the wind above the churning surf eighty feet below."
This rope bridge might seem treacherous , and it is. The goblins have rigged it so that if more than three Medium creatures (with a Small creature counting as a third of a Medium creature and a Large creature as three Medium ones) attempt to cross, the western supports tear free, dropping the planks down to hang vertically from the eastern rope and dumping anyone on the bridge into the waters below. A DC 13 Reflex save allows a creature on the bridge to grab at the remaining ropes (or leap to safety if it's within 5 feet of either shore). A series of knotted ropes at the base of the northern posts allow one to tie off the trap so that it can support many times the weight. (The goblins rigged the bridge this way recently when they hauled their unconscious horse hostage Shadowmist over the bridge.)
Originally, the goblins rigged the bridge so that it would fall completely into the water below, but when they tested it and realized that they'd stranded themselves on the island, they rebuilt the bridge so it would leave one rope connected, making it easier to repair.
Trap: Rigged Rope Bridge
Type mechanical; Perception DC 15; Disable Device DC 15
Trigger location or manual; Reset manual
Effect 80-ft fall into water (2d3 nonlethal plus 4d6 lethal); multiple targets (all creatures on rope bridge); DC 13 Reflex save avoids fall