Batman: Arkham Origins
49 Achievements
80-100h
Air Marathon
Glide 26 miles total
32.5%
How to unlock the Air Marathon achievement in Batman: Arkham Origins - Definitive Guide
On the other hand, if you're interested in grinding for this, I'd suggest doing it from one end of the bridge to the other, going back and forth until the achievement unlocks.
Good luck!
This is most likely impossible to miss while going through the story, doing side missions and collecting the datapacks. I got this naturally around 3/4 into the story. You don't need to worry about this.
This achievement will come naturally as you progress through the main storyline and work on the various side missions available. As a general reminder, make sure to glide around Gotham when going to your next objective, instead of using the fast travel points.
You will most likely unlock this achievement very early on in the game since some of the earliest story missions require you to glide around Northern Gotham countless times in order to track down the Penguin's location. Another great mission that will net you some more miles towards the achievement is Anarky's Most Wanted mission. As soon as you leave Penguin's ship, talk to Anarky's follower on the catwalks and you will need to glide back and forth around New Gotham and Old Gotham when disabling the three bombs. Since the bombs are so far away from each other and you will find yourself going back and forth down the Pioneers Bridge, the achievement will most likely unlock at this time. If not, keep gliding around during your playthrough, and you will obtain it in no time.