The patsy comes to the Cearlian Waste

"Follow the Patsy" is an "Expert" level adventure where you escort some droopy-eared goof through "hitherto unmapped" territory. Implicit is that the monsters here aren't as strong as the monsters in the next adventure on, which are 73 hp / 10** HD Boneless and Elemental Drakes. So this one is good for 4th level...

... unless it's played in the locations it's been assigned to.

This adventure's examples are the North Sojourner river and the Continual Rain cavern. Both are northwest quadrant - both also, coincidentally, flow from volcanoes (although they didn't set Skullhorn on the map). That terra isn't wholly incognita, to the elves, first because both the river and the cavern lie in territory core since 800 BC, secondly since the patsy is (especially if chasing a MacGuffin) following a trail in "an old book". If that book had maps, nobody followed up on those maps. BTW this blog allows for a dark-age deep in core territory before the shamans brought enlightenment.

Sargent and Thomas were veterans of RPGs, if not for D&D itself, so were already aware of what bores players. Fetch quests and grinds bore players. Hence, why the comic-relief NPC. As for what's fetched here, the usual MacGuffin in GAZ13 is the Soul Crystal. By this point in this Gazetteer, the two authors must have realised that this plot-device was getting well-worn. So the plot does allow for other motivations - or just the joy of exploration.

If you've seen the map we got, in the core regions both the North Sojourner and the Continual Rain waterways have their headsprings not beyond to the north, but to ABOVE. This would rule out soul-crystals being the MacGuffin.

But there can be nuance around the waterway which runs northwards of the Cavern of Continual Rain. To some, this looks like an author thinking of the Lethowan.

To Desrii Castle, the Lethowan runs from due north, skirting the Continual Rain and Sethandor to the river's east. Upstream it flows through Bethlandor Cave - as the old book calls it. Beyond that, is muddy Caerlinyl Lake; or, the explorers can take a "tertiary" tunnel to a vault to the east.

As you know, I am not invested in "canon" maps that haven't been explored in canon. I'd be fine with pushing Caerlinyl further north, or northwest or wherever. That vault with the Cearlian Wastes, though, is designed to tunnel out to the North Sojourner between the City and New Grunland. I can't budge it. Also if Desrii was worth a castle, that goes double for this region.

I think Darkleaf Bastion is outpost for a now-dead colony. That tunnel from the Lethowan was a canal; and so the Old Book describes it. Since then the canal has silted up, leaving enough moisture for the Oakstalk, but not for the Cearlian beyond. Somehow the region has avoided attention.