I need to wipe out a city. Not a huge one (I won't let them grow beyond a certain limit), but big enough to need to do some pretty serious damage. Let's say something similar in size to Pompeii. (yes... that Pompeii...)
My weapon of choice is a meteor. Carefully aimed, let it meander the heavens for millions of years and then ----blam!---- right on target at the appointed hour with no need of any further intervention.
Clean, clinical, and no side effects.
Only there are side effects, aren't there...?
Oh sure, a nice small meteor can make a beautiful explosion and a nice crater for itself without really having any effect on anyone outside the blast radius. But when you scale up, a bigger meteor will not only make a crater but also mess with the local or even global climate, maybe even trigger tsunamis, earthquakes, volcanoes...
Argh! I don't want any of that. All I want to do is wipe out a city with a giant space rock, but leave everything else untouched. No collateral damage. Is that really too much to ask?
Ideally, I'm hoping for a lone survivor to get away because he just happened to be leaving the city immediately before the event (uh... because I'll tell him to. Hope he listens!). The exact distance away isn't important, but he needs to be able to turn around at the right moment and see the impact close enough at hand to know exactly what happened but without getting caught up in it himself.