Northwest of Dublin near OldCastle, the Mullaghmeen Forest has singletrack and fire roads open to mountain biking. To reach the trailhead from Dublin, follow the N3 northwest to Virginia Road. Head northwest towards Oldcastle. In Oldcastle, head for Mount Nugent. After bridge, turn left to Katsie Brownes. Continue for 3 miles past Katsie to car park.
Overall, Mullaghmeen Forest is the 6th most popular mountain bike trail of all 14 mountain biking rides in Ireland.