Robert E. Howard’s “The Black Stone” is regarded by some as one of the finest mythos stories not written by HPL himself. The full text is available online here. This story introduces REH’s fictional book “Nameless Cults,” it’s author, Friedrich Wilhelm von Junzt (German, 1795-1840), and the mad poet Justin Geoffrey (American, 1898-1926):
“They say foul things of Old Times still lurk
In dark forgotten corners of the world.
And Gates still gape to loose, on certain nights
Shapes pent in Hell.”
It also mentions Otto Dostmann and his book, “Remnants of Lost Empires,” (Berlin, 1809, “Der Drachenhaus” Press).
The titular Black Stone is located outside the village of Stregoicavar in Hungary. This town is said to be 3 days’ coach ride from Temesvar. Stregoicavar is fictional, but Temesvar is real. Today, it is inside Romania, near the Hungarian border, and is known as Timisoara. Here is its location:
Here is the same map with a 60 mile radius drawn around Temesvar. This is my guess at the range of a 3-day coach ride in rough, hilly country. Stregoicavar should lie within a few miles of the edge of the blue circle: