Some wild country in northwest Kosovo and eastern Serbia, with two tiny settlements and little infrastructure. These areas are somewhat easier to design, though the proliferation of mountains takes time. I look forward to the big open plains of the Ukraine, with nary a hill ... though when I return to that, I'll be missing mountains.
All of these territories for the last couple of months, with the exception of "Cattaro" on the last post, which is under control of the Venetians, are part of the Ottoman Empire. Despite the geographical obstacles before them, the Ottomans did very well in capturing and maintaining these regions for five centuries. This left an indelible mark on the land, both in culture and in the manner of financial expenditures and religion. In the game world, these lands are fraught with repression, religious persecution, blood feuds and political corruption.
The hillpeople, who hated the lowlanders, adopted Islam and become Moslems; the lowlanders remained steadfastly Christian ... though because they were isolated from both Catholicism and the Russian Orthodox entities, they formed local orthodox or catholic chapters that remain independent to this day.
As a pattern for designing game adventures, I find this difficult for my players. Most aren't invested in either religion or nationalism; it can be hard even for adults to engage in struggles based upon this region's abject hatred for that, on a degree that often seems absurd. Western soldiers in Kosovo in the 1990s had trouble relating to people's motivations that were based on wild, unrestrained hatred and a desire for genocide — both of which are legacies from such a long time under Turkish rule, where the locals had little control over their futures or social change. The absence of political control fosters petty discontents. The 17th century Balkans are rife with it. Player parties are not, and it's therefore with blank eyes that they respond should I introduce some narrative based on this village attacking that without apparent cause. So I largely don't. Too much of it and all the parties want to do is leave and so somewhere more sensible, like France or Scandinavia.