This review may contain spoilers. I can handle the truth.
Aliki Koutoura’s review published on Letterboxd:
This review may contain spoilers.
This film is a pure cinematic experience. The stills are beautiful (just like old photographs) and the format totally serves the isolated atmosphere the director wants to emit.
The film messes with your mind from the beginning to the end. Do not expect answers regarding certain incidents taking place, such as "Is this real?", "Is this taking place in the past, the present, or the future?"; besides, the director himself admitted that the film is open to various interpretations.
Personally, I believe the whole film is a metaphor and none of this existed, as in the final scene we witness a fogy, empty landscape, without any buildings around. It's like everything takes place in Ephraim's mind and the two keepers are just different sides of the same coin. Apart from the fact they both have the same name, it also seems like they are responsible for the death of two people. However, they both claim the deaths happened by accident.
At some point, Ephraim confesses that he wants to start fresh and leave the past behind. Therefore, he could have possibly repressed the fact that he killed his partner and twisted the events in his mind, in order to persuade himself it was an accident; memory is a complex process and it is often possible to remember an event not necessarily the way it actually occured.
It seems to me that the top floor of the lighthouse represents the idea of self-knowledge and truth (I dare say that, from this perspective the lighthouse operates somehow like Plato's cave). When Efraim finally gets there, he simply cannot escape the truth anymore and gets totally mad.
Finally, the annoying seagull could be interpreted as the last trace of sanity left in him; it's his consciousness, reminding him of what he did.