I tried to check the Prince of Wolves Pathfinder Tales novel, but the account of the journey abruptly picks up a few days after leaving Caliphas and encounters plot at the Monastery of the Veil, then just as abruptly cuts to Kavapesta.
If I were to speculate a proper route from Caliphas to Ardis, I would start travelling up the coast to Vauntil (small but relatively scenic town). From there I would probably continue all the way along to Thrushmoor (large town). From there it's due north along the Danver River and into the Hungry Mountains, passing through a couple more towns.
From there obvious geographical landmarks for the road get a lot more hazy because typically roads do not suffer mountain ranges lightly. The Pathfinder Tales novel is useful in suggesting that the road to Kavapesta does go through the small county of Ulcazar for a bit before arriving at a bridge across the a gorge formed by the Senir River. Additionally Wait's Span is a tiny hamlet which also claims such a bridge despite the town being mostly burned down and may be pertinent to a trip.
I feel like the trip must inevitably cross into the city of Kavapesta depending whether or not the plague is in season, then after that I suppose it's a straight shot along the Vhatsuntide River to Ardis.
The most comfortable portion of this journey feels like the travel up the coast and river, getting considerably rougher in terms of the comforts of nearby civilization while crossing the mountains and the tiny mountain villages, until it reaches the far side.
This trip I'm eyeballing based on some map data, I'm going to say at least two weeks on foot. The journey appears to stretch a flat 120 miles to Hyannis, which is probably 6 days travel, while the north side of the mountains adds another 60ish, for 3 more. The rest depends on how passable the mountains are at the time of year and how much time is lost winding around valleys. Travelling by carriage in ideal conditions might cut that time down by up to a third, shaving at 3-4 days off the itinerary.
PS. I originally considered the path of the Raiteso River more likely until I realized that the Chateau village up there was only a tiny hamlet with unfriendly attitudes to anybody peeking in on the countess' private affairs. Meanwhile, for travellers seeking to avoid the mountain passes, their only recourse are the equally undesirable or worse routes either through the foothills of Amaans, directly in the shadow of Virlych's unnatural climbs, populated only by small hamlets (at least as far as the maps show us) or a circuitous route that goes as far as Carrion Hill, and still is forced to cross the mountains at some point if it doesn't trek directly through the haunted Furrows.
Thanks so much for such a detailed post. I really appreciate you taking the time to look into this. I am not nearly as versed with Pathfinder lore as you, but from what I could tell I was really surprised on how difficult it was to travel from Ardis to Caliphas. I can see why they wanted to relocate the capitol.
It occurred to me after posting that the difficulty could indeed also partly explain why Ardis is so filled with neglected and dilapidated estates. Especially after the capital moved to the bigger city, there was not enough motivation for folks to return to their homes across such a difficult trip
Ah, good point about river travel being inherently preferable where able, though I think it may not necessarily be more ideal?
Travelling the Path would involve tacking up river (perhaps not as slow as on foot, I wager?) into what is likely the single most dangerous land in the country, with weather capable of draining fluids, inflicting mummy rot, striking with literally unholy lightning, or simply pouring acid rain upon the unprotected.
Even if one purely skirts the edge of Virlych, Ghorcha pass is long and widely rumoured to be heavily haunted in the shadow of Virlych, with few if any noteworthy settlements. Furthermore, the only place to secure a boat short of carrying it across the pass on foot (the population of Amaans is noted as primarily 'clinging' to the opposite side of the pass from Virlych) is Ruwido, inhabited almost entirely by outcasts.
From there the trip should be easy, as it is all sailing down river to Ardis, but I feel as if the extraordinary risk of travelling near Virlych, much less the social perception of the county, more than make up for the benefits.
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On the other hand, the fast and treacherous Destach river is much more plausible of a journey. That said, Illmarsh is a dilapidated hovel of a town (though it wasn't always--the gold brought up by its fishers made it wealthy once, albeit at the cost of demon worship) and Redleaf is but a tiny village. If you choose to brave this route, however, you are rewarded with a stay in Carrion Hill, one of the more populous Ustalavic cities, if more than a little strange. From here it's rough terrain through a valley not given a name I'm aware of, where you can rejoin the path I presented just north of the Monastery, unless you choose to go through the haunted Furrows.
(Yeesh, Ustalav has at least a couple 'rumoured to be haunted' regions, for I suppose obvious reasons)
How the traveller rates these routes probably differs based on their reasons for travel. Adventurers of some renown are much more likely to see the haunted Ghorcha Pass or Furrows as fair game and gladly take the circuitous routes. My original post spoke from the perspective of a traveller who sought to minimize danger and maximize the number of relatively populous and comfortable settlements between the two locations (a noble, perhaps, travelling from new capital to old or vice versa).
It really does seem like travelling into Ustalav beyond the coast is a challenging affair with few ideal avenues whether by foot or boat--which is somewhat reflected in the general rustic nature of the country, in contrast to its only somewhat metropolitan city, Caliphas on the coast. Only Ardis even comes close to matching it for population as the former capital.
oh yes, of course water travel is essential and considerably faster. The significance of Lake Encarthan as a trade hub is not lost on the nations around it, however it is probably of less concern to those traveling inland to Ardis. I can't deny it would be 100% preferable to take the river as far as it goes if all other things being equal, however I only mean to suggest that both the river routes suggested require crossing a significant stretch of land regardless, and at least one of those routes necessarily crosses the most inhospitable territory in the county, and so are less than ideal.