Cnoc na Péiste (Irish for "hill of the serpent"), anglicised Knocknapeasta,[3] at 988 metres (3,241 ft), is the fourth-highest peak in Ireland, on the Arderin and Vandeleur-Lynam lists.

Cnoc na Péiste is the highest point in the Eastern Reeks section of the MacGillycuddy's Reeks range, which consists of a long narrow ridge that takes in several summits before ending at Cruach Mhór 932 metres (3,058 ft) and descending into the Gap of Dunloe, to the Head of the Gap, only to rise up again towards the Purple Mountain Group.

[4][5][6] To the southwest of Cnoc na Péiste is the peak of Maolán Buí (973 m or 3,192 ft) and a generally flat grassy ridge to the col at the Devil's Ladder.

[4] A stream called Glasheencummeennapeasta flows northwards from Lough Cummeenapeasta into Hag's Glen, to join the Gaddagh River.

[13][14] At about 7 am on 17 December 1943, during World War II, a United States Army Air Forces (USAAF) plane crashed into the northerly face of Cnoc na Péiste.