Breakdown of Na sajam dolazi mnogo posjetitelja.
na
on, at / to, onto (with motion) / about (thinking about)
mnogo
much, a lot of (+ genitive)
dolaziti
to come
sajam
fair
Questions & Answers about Na sajam dolazi mnogo posjetitelja.
Could I use mnogi posjetitelji instead of mnogo posjetitelja here?
Yes, but the grammar of the rest of the sentence would change. Mnogo is an invariant quantity word that forces the noun after it into the genitive case (posjetitelja). If you use the adjective mnogi (many), it has to match the noun in case, gender, and number, so you would say mnogi posjetitelji.
Why is the verb dolazi in the singular when the meaning is plural ('many visitors')?
Because the grammatical subject of the sentence is the quantity word mnogo, not the visitors themselves. In Croatian, quantity words like mnogo, malo, and numbers from 5 upwards require the verb to be in the third-person singular. If you used the adjective phrase mnogi posjetitelji, the verb would be plural: mnogi posjetitelji dolaze.
Why do we use the accusative na sajam instead of the locative na sajmu?
The verb dolazi (comes) implies motion toward a destination. When the preposition na indicates direction or motion to a place, it requires the accusative case. If you were talking about a static event happening at the fair, you would use the locative case: na sajmu.
Is posjetitelja a singular or plural form here?