It starts well, with the opportunity to develop into something interesting and original. Sadly just at the moment we finally get to the core, where things should stop being mysteries and some unraveling should occurs, the story just stops and it becomes a quite long voiced over epilogue that brings absolutely nothing. This is absolutely shitty. Not only on the scenario, but as a directing choice too, and it ruins not only the story but also the whole concept. Really catastrophic.

The story is interesting, specially with the trap intro that sells you way more than the movie is willing to offer. Such a shame that it leads to nothing in such a shitty way.

Basically imagine Dark (https://trakt.tv/shows/dark). A kid disappears. Then another. They find a weird corpse. We get a shot of the kid entering the cave and the weird thing happening inside. And cut to a 20 minute voiced over showing how the family's life ended miserably because they never found their kid. The end. This is **exactly** that.

So many questions that can't really be considered "left open" because they clearly didn't even think of anything for them.

The most lazy and disappointing thing is that we know there are [spoiler]different timelines[/spoiler] people involved. But was there just another one ? Many ? Why were there here ? It's not that they just discovered it and ended there, they clearly had an agenda that involved, or at least justified, killing people (and even [spoiler]kids[/spoiler]), and not just any people, but [spoiler]other versions of themselves[/spoiler]. However there is not even a hint of the existence of any reason for that. Best assumption is that they attempt to prevent knowledge of the theory for others ? But that would be such a weird way. Was there even an agenda or did they just happened to end there ?

The moment things stop is when Johannes is [spoiler]shot in the cave[/spoiler]. That's when things should have started to explain themselves or become weirder. [spoiler]Did this create another reality, splitting between the one where she shot and the one she doesn't ? Which one are we following afterwards ? The original ? Another one ? Was he transported to another timeline ? Did his change ?[/spoiler] Instead we get nothing at all.

The two supposed [spoiler]main timelines[/spoiler], assuming there are only two, are not even that close since there are major differences in the characters involved a lot of years ago ([spoiler]Karin's and Johannes's mother's survival for instance[/spoiler].

Why no [spoiler]Johannes alternate[/spoiler] ?

[spoiler]Karin know him, but he also feels like he knows her[/spoiler]. Only hint at a possible unconscious reciprocity between versions... but left totally unexplored except for this.

What's the [spoiler]recorded piano[/spoiler] nonsense at the end ? What ? He went around recording in the cave and somehow got that ? Why would it be in the cave ?

Some weird inconsistencies, like the receptionist seemingly not knowing [spoiler]the existence of Karin[/spoiler], which could be justified by some weird phenomenon if we weren't shown that at the same times other people are perfectly aware (like the other musician).

Also maybe it didn't need the extra of him ending up dating a girl less than half his age that he met, as an adult, when she was 6 years old ?