Fabian has produced an elegant distillation of Mikelmerck here.
We got on a bit of a roll again and batted more ideas around for what kind of dangers such a place might have. Mechanically, adventuring sites are many.
Ruined (or inhabited) castles - this is border country
Out in the wilds - notoriously hard to run I find, but so much fun when they work
Village crawling and investigation - Mikelmerck has only two or three places that could properly be called towns
Fetch quests are a given in this far-flung land where ordinary people simply don't want to go away from whatever it is they'd rather be doing
Underpinning all of this is the sense of life going on. Nothing much seems to happen on the surface in Mikelmerck - people get on with their lives and do the things they've always done. It's a tough life, but the land is beautiful and the inhabitants feel deeply possessive of it. All the time of course, they're holding the boundaries, but not in any very conscious way.
The festivals and events that hold life together are mostly local. The Nine Men of Muriz happens every year, but the performances only concern the village of Telrick.
Performance of all kinds underpin many of the warding rituals. Boothler Samael the mage understood this and built performance sites around Mikelmerck on specific nodes. His traveling band of mages wandered the route performing as they went and keeping the boundaries true. Not at all coincidentally, this was a period of stability and growing wealth for Mikelmerck. Now all but one have long gone, and the last may be under threat. Again, it is not coincidence that disease is breaking out more frequently and the needed visitors are not coming in such profusion.
Visitors matter to Mikelmerck. How else is the glory of the Duchy to be maintained unless it is seen?