I am searching for an adult (urban) fantasy novel I read a few years ago, but can't remember the title and author.
It takes place in a (17-18th century-like or late medieval) world in which there exists some kind of guild using a kind of magic which requires meditation and going to some sort of dream-like spiritual world to collect "spiritual energy". There is also an opposite, dark, dream-like world, in which you find a gigantic tower full of monsters or dark entities, and which is called "Umbra".
The main protagonist is a young women whose ancestor (mother? grandmother?) was part of this guild. She is saved(?) by the members of the guild who teach her how to use magic, and prepare her to fight an enemy who also uses magic.
This enemy was trapped in the world Umbra while meditating and thought it was the first dream-like world which I talked about earlier. His goal is to get to the highest part of the tower to meet what he thinks is God, but actually is some kind of "demon king" who will destroy the world if released.
One more detail that may ring a bell: the first dream-like world looks the same as the real world (but is more "dreamy") and contains some kind of gigantic fall at his end (meaning it is a flat world?). Also, I remember the members of the guild think that this fall is actually where people go when they are dead and that this is also where God went (and from which he never came back).
Finally, to complete this, I know there is at least one more book written by this author, and which takes place in the same world, partly in parallel to the first book's story. I think the main (male) protagonist of this second book is the character with whom the character of the first book was in love. Moreover, there is a part in which we follow her into an island, meeting with a (mysterious) masked character who ends up being this guy.
The island in which this part of the second book takes place is some kind of natural habitat for wild dragons. Because, yes, there are also dragons in these books, but they don't have a very important role in the story, if I remember correctly.
The books I read were actually translated into French.