I have been thinking about Trokair from the perspective of a Western Marches-style sandbox game over the past week. I never get really far (as is my custom) but I have made bits of progress (the giant oyster from last post came from my musings).
A Western Marches game requires dungeons and challenges to exist prior to the PCs' arrival. It also requires those challenges to develop without recourse to human settlements as no civilized PC races inhabit the world beyond the safe zone of the home base. This rules out many of the typical plot devices used to drive adventure (kidnapping, recovering stolen property, immenent threat of attack, etc). So I have been forced to explore why PCs would push on through dangerous environments and continue forth in any given dungeon locale. There is no captive townsperson at the end of the dungeon. There is not necessarily any great treasure or macguffin under the watchful eye of the Boss Moster. Players really need to desire exploration for its own sake, an increase in character power through experience, and the acquired treasure that may or may not be found in the dungeon (and maybe, like myself, just the opportunity to roll dice and kill things; I wonder how long that motivation can carry other players?).
Impressing players from the start with the concept that their characters are explorers and adventurers is probably key to this kind of game. They are the kind of people who see a cave and need to know what is inside it, what lies around the next bend, what might be behind that crevice just large enough to slip through. They kill the monsters they encounter to protect themselves (it occurs to me that the monsters need to be hostile as a matter of policy; they could be angry because the PCs have invaded their home but animosity should be assumed at all times to drive the conflict). If they find treasure, that is a good day.
From another angle, the presence of dungeons has to be explained through some means. If this is a land new to the PC races' knowledge, how did catacombs and sewers and other such locales develop? Most likely, one of three methods would be used to populate the wilds with dungeons:
1. Adventures are almost entirely wilderness based, with natural caves and humanoid forts making up the difference.
2. A prior civilization inhabited the land but has declined into ruin and the PCs are exploring their forgotten empire.
3. The PCs' own civilization once inhabited the land but it was overrun and they are now going back.
Option 3 is basically a subset of 2 but it introduces a slightly more cogent motivation for the PCs by sacrificing a bit of the unknown. I am currently mulling a combination of 2 and 3 to incorporate some ideas from Trokair. The actual ruins of Trokair might be known to the PCs but they date from an earlier, extinct civilization (and many of the dungeons to explore also arose from that civilization). However, there would also be a few more recent places, like Land's Blessing (the town just outside the Hoach).
The basic idea at the moment is that the PCs' people arrived from across the sea some years ago and established a settlement on the coast (Wyndhaven). They sought to expand but encountered heavy, unforeseen resistance by various savage humanoids (orcs, goblins, etc). For years the colony was essentially under siege, with sightings of the humanoids on the horizon deterring any attempts at expansion. The town was waiting for further men and supplies when something happened to curtail or delay that reinforcement (a war back home thta diverted manpower, a need to build up resources after the expense of the first colonization, etc). They consolidated their holdings and decided to wait it out. One day, no more humanoids were sighted. After a few more months/years, a group of settlers set out to found a new town called Land's Blessing (it was the only fertile patch of soil in an area known as the Thornscape). The town flourished for a while before the humanoids returned and wiped it out. Now, no settlers venture out of Wyndhaven.
The majority of dungeons would arise from the Trokairian civilization. However, a few settlements close to Wyndhaven would have come from the settlers and might hold options for human-related adventure (kidnappings from farms near Wyndhaven, criminals on the loose from Wyndhaven, stolen goods, etc). I like compromises; they seem to open the most doors.