I read the novella about 5-6 years ago, but I do not know how old it is. I am also not sure, if it was written in German or English. In any case, it was quite short, maybe 150 pages and I had to order it directly from the publisher instead of Amazon e.g.
The story was about a boy who worked on a ship as an assistant to the cook. During the journey the ship probably "switched dimensions". In fact, I know quite less of the start and the middle of the book. The crew descended slowly in to madness, maybe there was cannibalism.
At the end however - and I am very sure about this - the boy and the cook find a volcano and ascend it. On the way up they see all sorts of petrified humans. As they reach the rim they see a gigantic eye which fills the complete volcano. In horror they try to flee only to become petrified themselves, but staying alive within and forced to contemplate the eye for eternity.