According to Wikipedia:

Sisu is a Finnish concept described as stoic determination, tenacity of purpose, grit, bravery, resilience, and hardiness. It is held by Finns to express their national character. It is generally considered not to have a literal equivalent in English (tenacity, grit, resilience, and hardiness are much the same things, but do not necessarily imply stoicism or bravery).

Our main character is an old man, out looking for gold in Lapland toward the end of the Second World War. The opening voice-over explains (the whole thing is in English, despite the setting and cast almost all being Finnish) he's "left the war behind." He finds a lot of gold, but some retreating Nazis (who also have a truck full of captive women, they'll be important if you actually watch the movie) find him and decide to take his gold.

That's it for the plot. What, you were expecting more? They find our main character very, very hard to kill. And he's very skilled at killing them. People get knifed, shot, exploded, and hanged. It's all good fun.

It seems my taste for bloody mayhem is receding as I age. This was ... well, not "too much" for me, but it didn't really appeal. And I had a lot of issues with our anti-hero's durability. They make the point in the movie that this guy is a legend to both the Germans and the Finns, and that his nickname is "Koschei" ("the Immortal") and he simply refuses to die. But if you view him as human (as I made the mistake of doing), there's no way he could have survived what happened to him. So ... this should be classified as a "Superhero" movie - he ain't human. And if you do something silly (as I did) and stop and think about his motives ... well, the only thing our main character cares about is his gold. Not the war, not human rights (although he does show some slight sympathy for the female captives), just ... "I want my gold back." Not very appealing, just a vehicle for carnage.

This is the work of Jalmari Helander - and I'm mildly embarrassed to say I've seen his entire filmography. Not that that's hard when it consists of three films (the other two being "Big Game" (2014) and "Rare Exports" (2010)). The first movie starred a very young Onni Tommila, the second starred Onni and his father Jorma. This movie stars Jorma, with Onni in a still-prominent role. All three movies are both absurd and bloody. They're all mildly interesting but none is great.