This is the 16th most frequent Icelandic word.
upp
"Upp" means "up" in English.
In this sentence, "upp" is used as a preposition indicating upward movement or direction, literally meaning 'up'.
Hann gekk upp fjallið án þess að stoppa.
He walked up the mountain without stopping.
Here, "upp" is used as part of a verb phrase to indicate the completion of the action 'waking up'.
Við vöknuðum upp við undarlega hljóð.
We woke up to strange sounds.
In this example, "upp" indicates a higher relative position or movement upwards to the shelf.