How do you pronounce للمطعم ? Lil maT'am, as if the preposition were li...? or else how? lal?
Lil maT3am.
We almost always use ِل (the shortcut of إلى) when a displacement is implied (some people use على). Now I think my example wasn't the best suitable, we wouldn't say خرجنا للمطعم since خرجنا means "to get out of something". We would rather say مشينا للمطعم but خرجنا من الدار (we went out of home). And it is the most common verb in Morocco as well for exiting.
طلعنا or its antonyms, هبطنا/نزلنا/هوّدنا (literally "to get down") are also used but it means "to go somewhere" though مشينا or رحنا (in the East) are used as well when a displacement is involved.
Regarding the preposition, it is خرجنا من if I want to say that I went out of some place.
Edit: I read again my post and I certainly confused you with all of the possibilities

. You can just stick with مشينا للمطعم, it is probably the most frequent way you will hear it.