The Carneddau from near Pentir. Yr Elen centre with Carnedd Llywelyn behind, Carnedd Dafydd right.

Carnedd Llewelyn, also spelt Carnedd Llywelyn, is a mountain in the Carneddau range in Snowdonia, Wales. It is the highest point of the Carneddau and the second highest peak by relative height in Wales, and lies on the border between Gwynedd and Conwy.

Topography and ascent routes
Carnedd Llewelyn lies in the middle of the main north-east to south-west ridge of the Carneddau, between Carnedd Dafydd to the south-west and Foel Grach to the north. A short subsidiary ridge links it to Yr Elen to the north-west. Its position means that any route to this summit involves a long walk. It can be climbed from Gerlan, above Bethesda, taking the path following Afon Llafar then continuing to the summit of Yr Elen before following the short ridge to Carnedd Llewelyn. Another path starts from Helyg on the A5, taking the track to the reservoir then following the slopes above Craig yr Ysfa to the summit. An alternative is to reach it by following the main ridge, either from Pen yr Ole Wen or from Foel-fras.

Though the summit, like that of many of the mountains in the southern Carneddau, is a flat, boulder-strewn plateau, the cliffs below the ridges are well-known rock climbs, notably Ysgolion Duon (meaning "black ladders") and Craig yr Ysfa.

Name
Carnedd Llywelyn means "Llywelyn's cairn" in Welsh. It is widely believed that Carnedd Llewelyn and the neighbouring Carnedd Dafydd are named after Llywelyn ap Gruffydd and his brother Dafydd ap Gruffydd, the last independent prince of Wales, respectively. An alternative theory is that the twin peaks are named after Llywelyn the Great, an earlier prince of Gwynedd, and his son and successor, Dafydd ap Llywelyn. Other sources cite a combination of the above, i.e. Llywelyn the Great and Dafydd ap Gruffydd.

The spelling of the name is also controversial. Carnedd Llewelyn is the form used by the Ordnance Survey, the national mapping agency for Great Britain, and by many other sources. Locally the spelling Carnedd Llywelyn predominates (it is used on the website of the Snowdonia National Park Authority, for example); this is also the form preferred by most Welsh writers, among others. The Welsh personal name Llywelyn, from which the mountain's name is derived, is always spelt thus in the Welsh language, although the forms Llewelyn and Llewellyn are found in older English-language sources.

Cultural references
The mountain features in Welsh poetry and literature; the earliest known work is a poem by Rhys Goch Eryri, Carnedd Llywelyn, composed c 1400.