My hubby got an itch to find the airport. We are both hunters, level 35 and 42 (at the time), and no mount or special potions or anything was needed. Below are some screenshots of our adventure including how to look inside the backdoor to IF. I am currently looking for lore to this area.
Here is a pic of the tanks
This is what it looks like if you go to the back door
All it is is a long tunnel with void at the end. I jumped my pig and he fell through the world and died after falling for about 30 seconds.