An ADIT is a horizontal or nearly horizontal underground passage used for access to a mine, and it is typically four letters long. A TUNNEL is a passageway that is typically constructed for transportation purposes, and it is six letters long. A stope is an underground excavation used in mining, and it is five letters long. Lastly, a PIT is a large hole in the ground, and it is three letters long. Together, these four words form the term 'mine feature, ' which refers to the various features found in a mine.