Deep Knowledge (Ex)
Replaces: Favored Terrain
At 3rd level, a deep walker gains a +2 bonus on initiative checks and Knowledge (dungeoneering), Perception, Stealth, and Survival skill checks while underground (in caves and dungeons). Every 5 levels thereafter, the deep walker gains an additional +3 on each of those checks while underground (to a maximum of +11 at 18th level). This ability replaces favored terrain.
