[SPOILERS] - Your scariest part of the game

[PathOS]

I would actually argue that the entire "Abyss" setting was pretty scary. I'd liken it similarly to The Prison in Amnesia, which to me was the "scariest" area of that game due to how dark it was with all the monsters.

Kudos to Frictional for making the Abyss area look so alien and inhospitable, with the currents looking like harsh winds, and the pervasive darkness all around you aside from the guiding lights.