[3] Two such antagonistic organizations are outlined: the Terra Arcana, an esoteric society dedicated to keeping the Hollow Earth a secret; and the Thule Society, based on an actual organization associated with the Nazi Party during World War II, who seek the powerful ancient weapons they believe are in the Hollow Earth.

[3] An introductory adventure is included that pits the heroes against a Nazi group racing to enter the Hollow World and recover a lost treasure.

[3] Hollow World Expedition was designed by Bruce Baugh, Brannon Boren, Patrick E. Bradley, Eric Cagle, Jason Carl, Jeff Combos, Jim Cook, Tyler Running Deer, Chris Goe, Ed Matuskey, Melissa McNally, M. Sechin Tower, and Steve Winter, and was published as a 256-page hardcover book published by Exile Game Studio in 2009 with cover art by Stephen Daniele and interior art by Daniele, Mike May, Aaron Nanto, Mark Selander, and Jeff Slemons.

Knight commented, "The game is equally suited to a long campaign, where even getting to the Hollow Earth involves several tense sessions, or one-to-three shot shorts.

Knight concluded, "the fast-paced, pulpy fun of Hollow Earth Expedition is as good as it gets in single-volume roleplay.