Book 3 of Dangerous Journeys
From the back cover:
"Six Worlds in One!
"This is the sourcebook for the fantasy milieu you've always dreamed of!
"The world of Ærth is hauntingly familiar, yet strangely mysterious.
"Visit Æropa's Avillonian Isles, which include mighty Lyonesse. See the "Dark Continent" of Afrik, travelling up the Nylle River, past Ægypt's four great pyramids, to the unexplored lands of the interior. Or cruise the long reaches of the Mare Ostrum which reaches from eastern Æropa to the steppes of Central Azir. And then there are the seven lakes of distant Vargaard...."
The Epic of Ærth also covers the mazes carved into the world's crust and the hollow interior where ancient life forms still dwell.