I feel like "at" should work. I know "at" usually translates to "na", but since a park is enclosed, it always takes "v". In English "at the park" and "in the park" most of the time mean the same thing.
Just to be clear...when the noun is the object of an action, the ending changes? So to say "I'm at the park" парку is used...But if you want to say"where is the park?" You then say де парк??? Because no action is involved?
Yes, but accusative -у is only used for feminine nouns (the ones that end in -а). Other neuter and masculine inanimate nouns have the same form as the nominative. Animate masculine nouns have the same ending as the genitive.