Southwest of Dolgellau, Erw Goed along the Mawddach Cycle Path makes a good base for exploring local trails. Try the mountain bike loop around Craig y Grut on the north side of the estuary, which combines 4 bridle tracks.
To reach Erw Goed from M6, follow M54 to Shrewsbury. Then take A458 into Dolgellau. Turn onto A493 into Erw Goed.
Overall, Snowdonia National Park is the 59th most popular mountain bike trail of all 93 mountain biking rides in UK.