Small World Underground includes 15 fantasy races with creatures and 21 special powers. Each player will control several creature/power combinations during the game – spending points to choose these combinations – and will use these creatures to claim control of various underground locations. Some locations contain relics or are designated as "places of power," and units must first be conquered before a player can claim these special benefits. At the end of each round, a player earns points for the areas they control, and the player with the most points at the end of the game wins. Small World Underground can be played on its own, but it can be combined with other editions of Small World. It is recommended that players be familiar with Small World before playing Small World Underground.