Theory of the Shadow [SPOILERS.]

[senataur]

The shadow is one of the hardest plot elements to deal with. You could even make the argument that it doesn't even exist. The only evidence we have of it is that Alexander told us it exists and we presume that it is responsible for the red goo and the deterioration of the castle.

The shadow story could have been a lie of Alexander's to get us to do his work and red goo/castle destruction could have been the result of Alexander opening a portal rift into another world.

The great thing about this story is the many different ways it can be interpreted. The numerous unknowns that like the dark corners of the rooms you are exploring only serve to intensify the fear.