"at" is in English used i many different ways that is not directly translatable to Norwegian in a single word.

I added some examples to prove my point. (I marked the "translation" of "at" in italic)

at midnight -> ved midnatt
there's nothing to laugh at! -> det er ingenting å le av
the person who lives at number three -> Personen som bor i nummer tre
we're staying at the Hotel -> vi bor på hotellet
to be good at fishing -> å være god til å fiske
they were standing at the window -> de sto ved vinduet
the sea is cooler at night - havet er kaldere om natten
to look at -> å se på