Shadow Valley Prison Delve Blueprint

[NaC| `NeckeD]

I just finished my first delve mission on shadow valley prison and was wondering where the chest with the blueprint is (I truly thought I'd get it after defeating the boss, turns out it doesn't)
I searched the entire map, not kidding, I was using Ace and flying around above the abyss for more than 10 minutes and finally managed to find an unaccessible area with the blueprint chest!
I ran around the entire map again to try and find the door that leads there, no luck
Anyone has any idea how to get to it? or if it's bugged?

[Evanjellyo]

its a really wierd spot near the start with the cell maze, there is a drop off into black smoke, there you will find your entrance.

[NaC| `NeckeD]

thank you :)

[Crucial Notion]

Thanks as well, this really helped me.

[TAROU JP]

To explain in more detail, the entrance is located at the bottom right corner of the first stage.

[Marcus]

In first area when you get to the first cell maze if you go to bottom side of the cell maze, you can see on minimap there is platform yet you cant see it at the edge of cell area. tho you can see door there, you need to jump on that platform to access that door and there is secret area with the blueprint chest...

note: you can actually fall and miss the platform(on my first try I saw the door and fall on them yet I missed platform somehow so I search whole map to find the entrance and didnt find it then came back and saw the platform on minimap and this time I went from left side of maze and fall to side instead to bottom and tried to land on platform and this time it was success..)