Would love to get some input on this, too. "arbeider i havna", but "på en fabrikk". In another course there was the sentence "selger iskrem i butikken". Ok, but if you sit "på kaféen" it means you are doing something there, like eating or drinking, instead of just sitting there... This is very confusing.
I noticed on 'fabrikk' duo gives an 'ee' sound to the 'i', like a long vowel Am wrong in saying that proceeding a double consonant should give it a short vowel sound such as the sound in English of the letter 'i'?
(Seems pedantic I know but I'm trying to learn grammar and pronounciation too!)