The A4109 road links Aberdulais with Glynneath in Neath Port Talbot county borough, Wales.The route begins in Aberdulais at the junction with the A4230 and A465 roads; it diverges northwards away from the A465 up the Dulais Valley and crosses through the settlements of Crynant, Ynysfforch, Seven Sisters, Onllwyn, Dyffryn Cellwen and Banwen where it has a junction with the A4221.
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