When you are in Porto Fisco you will talk to Barry in the newspaper office about doing a daring act, and get a finger square. Use this by the rebel HQ on the scaffolding in the background on the right to get to the correct area.
When you have the rope further on in the story you are able to set a trap.
Once you've sprung the trap and are in danger, switch to one of the other characters to unlock this achievement.