Military aircraft do have a need to practice flying to the edge of their limitations and some of it may be near or over hamlets or small villages, perhaps these aren't considered 'built up areas'. All flying, though, in peace time is performed under strict rules with regard to height/altitude and location. Some of it may look hairy to the bystander as you don't normally see aircraft in that situation.
In my opinion, the best aircraft to watch flying around the hills is the A-10, unfortunately there aren't the same numbers around these days.