You are adept at maneuvering and fighting in tight spaces and underground passages.
Prerequisites: Base attack bonus +1.
Benefit: You do not take a penalty on your attack rolls or to Armor Class when squeezing into or through a tight space.
Normal: Each movement into or through a narrow space counts as if it were 2 squares, and while squeezed in a narrow space a character takes a –4 penalty on attack rolls and a –4 penalty to AC.
Special: A fighter may select Tunnel Fighting as one of his fighter bonus feats.
Source: Races of Stone, page 145.