Borrowing from films such as 'The Babadook' and 'Pan's Labyrinth', this beautifully shot film is less of a horror and more of a rich symbolic exploration of fear of the unknown.
The "beast" in this movie is like the monster Grendel from Beowulf: it is what lies unseen outside the door, and it what eats us from the inside. I watched it twice back to back.
The performances of Inma Cuesta and Asia Flores are sublime and deserve plentiful plaudits and awards. An excellent film and highly recommended.