Because Wurm is not a true 3D world, the cave layer is essentially a second world beneath the surface. It is possible to mine upwards and downwards with a few [[Mining warnings|limitations]].
* Mining straight mines at zero slope. Mining upward or downward mines at a slope of 20 in that direction. From this, a set of variants is applied based on skill which ultimately determines the final slope of the tile. This skill-based variance set is such that: <50 skill is +/- 3, 50-70 is +/- 2, 70-90 is +/- 1, 90+ is 0. Only the final action that breaks the wall (upward, downward, or straight) determines the direction mined.
* You may not mine upward out of rock and into the [[dirt]] that is covering it.
* You can mine downward until you reach the [[water]] table, but can not mine deeper than one tile level below water level.