It is often used as the 'boundaries' for each map, surrounding the edges of the level. It is also often used in campaigns as either a hint (especially in the earlier levels of Dungeon Keeper, where some rooms are surrounded by the rock in an unnatural square-shape.), or as a way of making the game more challenging, such as forcing the player to find another way around.
An interesting note is that in Dungeon Keeper, the location of Impenetrable Rock is always visible, unlike in Dungeon Keeper 2 where is it still hidden by the Fog of War until discovered.
| ||Claimed Path / Dirt Path / Gem Seam / Gold Seam / Lava / Reinforced Wall / Earth / Impenetrable Rock / Water|
| ||Claimed Path / Dirt Path / Gem Seam / Gold Seam / Lava / Mana Vault / Reinforced Wall / Rock / Solid Rock / Water|