I've heard of the fermented herring. And I have to ask Why !!??
It sounds like torture to me
I'd give surströmming or lutefisk a try. I was hoping to try hákarl when I was up in Iceland a couple of weeks ago, but never saw it in restaurants or in the one supermarket I went in (Bónus).
When lived in the US, it was in a region with a big Korean population, and I often used to go in the Han Yang supermarket. Once time, there were a few different varieties of jeot for sale, so I got a small tub of each to try. It's best not eaten by the spoonful on its own, the taste is far too strong. Better to use a small amount of it to add flavour to a bland kimchi or to boiled plain rice.