North of Drybone.
You won't see the passage in the map though because it's hidden but there's a cave you go through to reach the camp.
Dangerous aggressive monsters to look out for though.
Not Drybone, North of Drybone is the Golden Bazaar; the way to Bluefog is north of Black Brush.
The passage is North by Northwest from Blackbrush; you have to go up a ramp/cliff from the "yellow" section of the map to the "orange" section. The tunnel is then to the west. From there you can head up to Bluefog.
There are aggressive mobs on the way, but not all of them are aggressive. If I recall correctly, *only* the bird types are aggressive. The Ravenous Billygoats and whatever version of beetles/ladybugs are out there are not aggressive. The important thing is to get out of the twisting passages ASAP.