This is used in the quest for Thief's AF2 the Rogue's Bonnet. Climbpix Highrise is a thf-type mob and uses Perfect Dodge halfway through the fight. After defeating him you take the grapnel to another tower in the same area, remove all your equipment(EVERYTHING) and trade the grapnel to a ???. The tower you trade it to is random, but Climbpix always spawns from the same tower(SE most).
Wrong, it's the other way around. Climpix can spawn at any of the six towers (which one he'll spawn at at the time is random), but the one that you trade the grapnel to is always the one at I-7/J-7. I just did this earlier today and can confirm it. I also sent in a pic of the Grapnel. :)