My commute to and from the work is ~10km through the city, and there is very little bike infrastructure to speak of. It is not illegal to ride on sidewalks here, although it is not encouraged (the traffic rules state that one can ride on the sidewalk only if riding on the carriageway is too dangerous or impossible due to heavy traffic/jams/weather conditions etc., but there is no stated criteria applying to these, so many, if not most cyclists choose to ride on the sidewalk at all times).
I ride generally on the carriageway, mostly because it's faster and there are less obstacles on the road, but also because I rarely find the traffic conditions to be so troublesome as to avoid it. The roads I take vary from smooth to pothole-ridden to cobblestone. My tempo seems to be above average - I usually pass far more riders than they pass me.
Apart from that, I do some recreational/fitness riding, not shying away from gravel roads or forest trails - turns out my hybrid bike copes with those just as easy as my old MTB did. Just came back from such an after-work 60km ride a couple hours ago.