Head to the top of the Wonder Tower, either during the game or after you have completed it, and then glide forward off the ledge. Once you’ve gone far enough out, you’ll hit an invisible barrier and Batman will turn around. When he does, circle back towards the barrier again and keep repeating. If you go too low, Batman will shoot out his grapple and you’ll have to retry.
This achievement in Batman: Arkham City can be a tricky one to find. First you need to head to the church ner the center of the map, just North of the Restricted zone. Once there, head to the back alley –Crime Alley if you will– to find the chalk outline on the ground. Once you land, pay your respects and let the music play. Once it stops, the achievement/trophy will pop.