Long sieges can be a trial for both sides. For the beseiged especially, finite ammunition supplies always pose a problem - except when the ammunition can reproduce...
“ Small tavern in an out of the way town. Serve a wonderful delicacy that is simply outstanding. It is a creamy white consistancy, sweet, good to eat alone or a sweetener on any dessert.
If the explore or ask they are shown where they get it. They breed a group of large catipillars or some other type of insect that basically spit the product onto a setup that they created for that particular reason. Or maybe the delicacy is the byproduct of feeding them something.”
“ The PCs are sent with a diplomat to another country to protect him and do his bidding. There may be some espionage, rescuing, downright bullying, etc. Could make a nice medieval, special operations background.”
“ How about a dragon how cheerfully rules over a kingdom; his people all know him for what he is, and dragons are looked upon as wise and benevolent creatures. Dragonslayers from other kingdoms coming to free it from 'tyranny' are likely to get beaten to death by peasants with cast iron skillets.”