Thanks to a little-known and old-fashioned TV channel in my country (that admittedly has the residents of retirement homes as their main target group), I am rapidly becoming an expert in the domain of ancient films from Flanders - Belgium - that nobody has ever seen!
The question is if these obscure titles deserve to be seen, and in the case of "Kasper in de Onderwereld" the answer is a plain and simple: NO! It's a very dull and thoroughly unremarkable tale about a 30-ish mentally unstable man on an (endless?) search for his lost love. Is she dead? Did she even exist? We're not sure. He meets a lot of unusual people throughout his journey, and they are all surprisingly friendly and helpful. I didn't expect this, since the Dutch title translates as "... in the underworld", but everyone treats the protagonist with kindness and respect. So, basically, the film exists of lead character Kasper talking endlessly with a cemetery caretaker, a prostitute, a retired alchemist, a tavern owner, a construction site signalman, another mental patient pretending to be a journalist, etc...
Nothing exciting happens, really, and the film is only remotely interesting to see a handful of famous Flemish actors/actresses in their younger years, and to catch a glimpse of how typical communities in the Belgian countryside harmoniously lived together.