Katla is a slow burn atmospheric Icelandic drama/mystery/horror series that I fully recommend, but I feel like it has to be with the warning that if the past year or so has been rough on you then you may want to hold off for a bit. The series is a deep exploration on topics such as depression, loss, grief, and suicide, and its overall tone can be oppressively dark at times. I greatly enjoyed it because of that, but also it's the kind of piece of work that where need to be in the right mood to process its various themes.
Set a year after an eruption of the Katla volcano, the story follows the few people still living in the nearby town of Vík despite the health dangers. Various ash covered people start popping up in the outskirts of the town, all naked and in shock. In some cases they appear to be people who were previously missing or dead, while others seem to be younger doppelgangers of people who once lived in the town. All of these returning people force the inhabitants of the town to face their pasts in various ways, while the mystery of the volcano may connect to old myths of changelings.
The more linear and straightforward mystery of what is actually happening is honestly not the important aspect of the series, and it feels like a bit of an afterthought at times. This works really well for me because regardless of whatever explanation they land on (myth? science?) it simply doesn't matter. What matters is the collection of tightly woven character arcs as all of these people are trapped in a dark place of their own making and how they resolve their various existential issues.
This is all really pulled together by the tone and atmosphere of the town itself and the strength of the directing. Everything is covered in ash and there's a constant darkness on the horizon, creating a claustrophobic sense of being trapped despite the wide open spaces. There's an odd beauty in this darkness throughout, partly because of the camera work and breathtaking scenery and partly because of the sheer emotional resonance they build up with all of the various character arcs.
If you require a more straight forward narrative and solid answers in your mysteries then this may not be for you. As I mentioned, there's a certain point where you can tell the showrunners didn't really give a crap about the 'why' of what is happening, and instead wanted to focus on the 'why' behind every characters decision and their motivations. And as the focus on the story centers so much on various mental health issues, the answers simply can't all be straightforward. While some revelations are easier to interpret, we're left with others that are purposely vague and could lead to a number of answers depending on our own experiences. I appreciate that sort of storytelling, because in the end I believe it sticks with you more and makes you reflect on what you just saw.
Katla is a story about people being faced with the darkness in their lives and how they choose to live with that darkness or how to move on past it. Depending on where you are in your own life it will hit differently, and it can hit hard.