Dyffryn Mymbyr is a valley in Snowdonia, in north-west Wales, approximately 5 miles (8.0 km) in length, and leading up from Capel Curig to the Pen-y-Gwryd hotel.
The river Nantygwryd, originally called Y Mymbyr in Llywelyn the Great's charter of 1198, starts at Llyn Cwm-y-ffynnon, high above the Pen-y-Gwryd hotel, and flows into Llynnau Mymbyr going towards Capel Curig. The valley, like the river, lies both in Gwynedd and Conwy County Borough.
Today there are at least two active, hill rearing, sheep farms; Garth, featured in the 1967 BBC Wales documentary "Shepherds of Moel Siabod", and Cwm Farm.
The area commands excellent views of the Snowdon horseshoe, which (viewed left to right) takes in the peaks of Y Lliwedd, Snowdon (Yr Wyddfa), Crib Goch and Crib y Ddysgl.
The valley is the location of the Capel Curig weather station, which on many occasions has recorded the wettest weather in Wales [1].