Fantasy - A guy who discoveres the other world, he learns about becoming transparent and unvisible by mediatting in dark for long times and meets the spider Arachne (if I am not mistakken) in his dreams, trying to communicate with him

[Narek]

Well, all mentioned in the title.

I have read the book somewhere in 2012-2015

I remember the book contained a couple of stories, one being this one.

Not sure if the spider lord's name was Arachne, but it was very similar to that.