Afon Cych is a small river tributary to the River Teifi

River Teifi

The River Teifi forms the boundary between the counties of Ceredigion and Carmarthenshire in south-west Wales for most of its 75 mile length, flowing into the sea below the town of Cardigan. The catchment of the river is estimated to be 1,008 square kilometres yielding an average flow at Glan...

 in south-west Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. Its "official" source (although not its highest headwater) is at Blaencych 51°57′53"N 4°29′28"W. It flows north-westwards through a deep, wooded, secluded valley, and joins the River Teifi at Abercych

Abercych

Abercych is a small village of less than 100 houses, scattered mostly along the sides of a small lane that runs along the slopes of a valley in the north of the county of Pembrokeshire in South West Wales, in the parish of Manordeifi. It is an ancient village, the Welsh placename of which means...

 52°2′36"N 4°33′34"W. Its total length is 13 km. It receives numerous small tributaries: the Sylgen, Barddi, Mamog, Dwrog and Lŵyd on the east side, and the Pedran, Cneifa and Dulas on the west side. It formed the ancient boundary between the commotes of Emlyn Is Cuch and Emlyn Uwch Cuch, and it today forms part of the boundary between Pembrokeshire

Pembrokeshire

Pembrokeshire is a county in the south west of Wales. It borders Carmarthenshire to the east and Ceredigion to the north east. The county town is Haverfordwest where Pembrokeshire County Council is headquartered....

 and Carmarthenshire

Carmarthenshire

Carmarthenshire is a unitary authority in the south west of Wales and one of thirteen historic counties. It is the 3rd largest in Wales. Its three largest towns are Llanelli, Carmarthen and Ammanford...

.

The valley (Glyn Cuch) is well-known in Literature of Wales (Welsh language)

Literature of Wales (Welsh language)

After literature written in the classical languages literature in the Welsh language is the oldest surviving literature in Europe. The Welsh literary tradition stretches from the 6th century to the twenty-first. Its fortunes have fluctuated over the centuries, in line with those of the Welsh...

 as the place where, in the Mabinogion

Four Branches of the Mabinogi

The Four Branches of the Mabinogi are the best known tales from the collection of medieval Welsh prose known as the Mabinogion. The word "Mabinogi" originally designated only these four tales, which are really parts or "branches" of a single work, rather than the whole collection...

, Pwyll Pendefig Dyfed

Pwyll

Pwyll Pen Annwn is a prominent figure in Welsh mythology and literature, the lord of Dyfed, husband of Rhiannon and father of the hero Pryderi...

 has his fateful meeting with Arawn

Arawn

In Welsh mythology, Arawn was the king of the otherworld realm of Annwn, appearing prominently in the first branch, and alluded to in the fourth. In later tradition, the role of king of Annwn was largely attributed to the Welsh psychopomp, Gwyn ap Nudd...

, Lord of the Underworld. Boundary streams were often thought of as portals to the underworld.