Lestallum Back Entrance in Final Fantasy XV

You will need to fast travel to Coernix Bypass parking spot.

Fly northward in a Regalia type-F.

You have to fly as low as possible and turn around.

Fly around towards the tower shown.

Circle tower until you are going north again.

You need to fly just low enough to see the "land" indicator.

Press X now (street is darker here).

And keep R2 down, keep nose up.

After that, follow the street until you are near cliff.

Aim down towards the left guard rail.

And hold X immediately after you land.

Success! you are near the back entrance.

Note location on map and distance flown.

Now you will need to jump up this path.

You can use the daggers to jump higher.

And enjoy the view.

Head NE towards Lestallum.

You will hit an invisible force field wall.

That is Lestallum (near the front entrance).

After that, go this path to the back entrance.

This is a high spot, you should save here.

Then go down and go towards the forest.

You have to use daggers to jump across here.

Go northward toward the edge of the rocks.

Go north and right (look at a mini-map).

Jump up at this rock gap.

Go towards Lestallum after reaching the top.

Note that Chocobos are invisible here.

After that, you need to go northwards until you are stopped.

You will hit a force-field wall northward here. When you do, turn left and follow the wall.

Go left, hugging force field wall.

Now you are arrived at the back entrance (no force field).

Go under the bridge and see power crystals.

Arrived.