Breakdown of Мы долго сидели у костра и слушали истории путешественницы.
Questions & Answers about Мы долго сидели у костра и слушали истории путешественницы.
The preposition у (meaning by, near, at in a spatial sense) always takes the genitive case.
- Nominative: костёр (a campfire)
- Genitive singular: костра
So у костра literally means by/near the campfire.
The case is dictated by the preposition у, not by the verb сидели.
Долго is an adverb meaning for a long time / long.
Russian usually does not use a separate preposition like for in this meaning. You just add the adverb:
- Мы долго сидели = We sat (were sitting) for a long time.
- Он долго ждал = He waited for a long time.
So долго itself covers the idea of for a long time.