Orc's Drift

Orc’s Drift is a miniatures wargame depicting battles in the Centre of the Earth. In the late 19th century, brave explorers discover that the Earth is hollow – and populated by humans and assorted fantasy races.
– Orc's Drift introduction

Designer: Ty Beard
Publisher: A Fistful of Games
Year Published: 1999
Status: In Print
Contents: Archived online (24-page PDF)
Basing: I find that the optimum basing system is eight 28mm figures per stand (three or four for cavalry), based in 2” wide by 1” deep elements. A formed unit in mass formation will be 4” wide and 2” deep. In line formation, it will be 8” wide and 1” deep. In column, it will be 2” wide and 4” deep. Monsters should be on 2” square bases and heroes on 1” square bases. War engine s should be a minimum of 2” wide and as deep as necessary to accommodate the model. Since figures aren’t removed as casualties, your formed units can have any number of figures.
– Orc's Drift