Hollow Earth Expedition uses the Ubiquity rules, which were also created by Exile Game Studio. The main feature of the system is its use of binary dice pool rolls to determine success. Under the default rules, each even number rolled counts as a success, while odd numbers count as nothing. Odd 'nothings' do not cancel out even 'successes', making dice rolling quick and simple. This binary system has also led to the development of special Ubiquity Dice, which are not detailed below.
Game setting
The surface world
Hollow Earth Expedition is set in the 1930s. On the surface, everything appears as it does in our real worldhistory books, but if you dig a little deeper you encounter secret societies and villainous organizations, many of whom have a vested interest in the Hollow Earth. Two organizations are detailed in the main rulebook: the Terra Arcana and the Thule Society. Further organizations are listed in the first expansion, Secrets of the Surface World. The Terra Arcanum is an esoteric society dedicated to keeping the Hollow Earth a secret. They have their foundations deep in the mists of time, and only a few of their current members realize their true origins. The Thule Society are based on an actual organization associated with the Nazi Party during World War II. In HEX they have a deep interest in getting into the Hollow Earth and the powerful ancient weapons they believe are kept there.
The Hollow Earth boasts a wide selection of beasts and humans. Dinosaurs and other extinct creatures still live and hunt and are hunted by the various human groups who have become stranded in the Hollow Earth over the centuries. Not a great deal of detail is provided about the Hollow Earth in the main book, allowing Game Masters to customize the terrain to suit their campaign. Mysteries of the Hollow Earth expands a great deal on the denizens of Hollow Earth, including rules for beastmen of various sorts, and provides details such as a map and gazetteer for those GMs who want a more fleshed-out world, rather than the more nebulous "land of mysteries" from the core book.
Revelations of Mars expands the setting to include the dying and dangerous Red Planet.
Explore a desolate world filled with strange aliens, bizarre creatures, and ancient artifacts buried beneath its shifting sands. Discover xenophobic nomads roaming the wastelands, sky pirates prowling the air in their great flying vessels, and power-hungry warlords fighting over dwindling resources. Take shelter within one of the great walled city-states, and rub shoulders with haughty nobles, devout priests, and greedy merchants who plot and scheme therein.
