Hi,
Hobotheclown92's solution is spot on. However, I want to add some videos to the solution section of this achievemen. So this guide is meant as an addition to his well written solution!
This is a part of the main campaign and is unmissable.
*** Spoiler - click to reveal ***You have to make your way to the second airship and find Scarecrow. Before you find him you have to solve some minor riddles. And fight through some sneak passages.
If you need additional help, refer to the videos below:
(video credit: UKxJOK3Rx)
Hope this helps you guys :-)
Any improvements? Please let me know in the comments below!