In the depths of an Acheronian forest.    From Wordnet, Princeton University. 

Acheronian ... dark and dismal, after the river Acheron.    From Wordnik.com.  [The Volokh Conspiracy » Rivers and Words:] Reference

She did not care to dwell too long on what these Acheronian carvings might mean.    From Wordnik.com.  [Conan and The Mists of Door]

It had prevailed for more than a year since the last attempt of the king of Nemedia, aided by the revived Acheronian wizard Xaltotun, to wrest the kingdom from Conan.    From Wordnik.com.  [Conan the Avenger]

` Well, 'said Orastes, ` I am no Acheronian, but I am versed in some of the arts, and the control of certain spirits which have cloaked themselves in material substance.    From Wordnik.com.  [The Conan Chronicles]

Any closer and she might find the ground under her feet crumbling as the Mist fed on the traces of the spells of long-dead Acheronian sorcerers, like worms feeding on the bones of long-dead animals.    From Wordnik.com.  [Conan and The Mists of Door]

Like only Acheronian plate or also Acheronian cloth, Acheronian light armor etc.?.    From Wordnik.com.  [WarCry Network : Latest News] Reference

It simply signifies the ascent of the soul after death into the Olympian halls instead of descending into the Acheronian gulfs.    From Wordnik.com.  [The Destiny of the Soul A Critical History of the Doctrine of a Future Life] Reference

"Well," said Orastes, "I am no Acheronian, but I am versed in some of the arts, and the control of certain spirits which have cloaked themselves in material substance.    From Wordnik.com.  [The Bloody Crown of Conan]