6 hrs 40 mins
Leaving the car park entrance turn right and head along a single track road alongside the river, which will be on your left. You will be walking in a narrow, steep sided valley, covered in a blanket of tall pine trees.
Approximately a mile along this road you will pass a farm on your right, walk on through the gate and pass the pen enclosures. It is at this point the road passes over the river and the river now flows on your right. There are some small waterfalls along the way to the base of the dam, they look fantastic after a few days of prolonged rainfall.
As you reach a bend in the road and an old bridge crossing the river to your left, the huge dam wall of Grwyne Fawr will be in sight up head.
When you reach the gate at the base of the dam, walk through and cross over the foot bridge. On the other side of the bridge turn left and there are two gates. One gate straight in front of you and the other gate right next to it at the right. Take the gate to the right which will take you up a muddy path to the top of the dam wall. Take care ascending this path as there can be some water flowing and it is very muddy after prolonged rainfall.
When you reach the top of the dam wall you can explore around the dam and cross over to the other side. The views at the top of the dam are fantastic, as you look back down the narrow valley you have just walked. Have a look for the two reservoir triangulation pillars. Miniature versions compared to the Ordnance Survey pillars.
Once you are ready to carry on with the route, head back to the path where you reached the top of the dam wall and follow the path towards the gate. Once through the gate, turn back on yourself and take the gate next to it back in the direction from which you just came. This path gently rises alongside Grwyne Fawr Reservoir. The views along this path are spectacular. Keep your eyes open for the old, small water pumping house, which is now used as a bothy. It can be spotted just below the bank to your left as you pass through the gate opposite the rocky cliff face.
This path continues to rise for just over two miles. When you reach the summit, look for an open section to the fence on your right. The footpaths are quite well defined and it will be at a cross roads in the path. Turn right and walk through the open section in the fence line. This path will take you to the Ordnance Survey triangulation pillar Rhos Dirion. If a clear day the views along this ridge line are breathtaking!
Walk onwards past the trig pillar and follow the path along the ridge line. After a short time the path will slowly start to descend and the sharp rise of the Twmpa can be seen ahead. It is a steep climb, however it is only short and a quick stop to catch your breath and admire the view is always a bonus!
Keep following the ridgeline path and the road of Gospel path will soon be in sight up ahead. Drop down onto the road and cross over to the ascent on the other side to start the climb up to the Hay Bluff. Once you have reached the summit, again it is following the ridge line for half a mile, until you reach the Hay Bluff Triangulation Pillar. Time for a rest and admire the views before you head back along the route you came following the ridgeline.
Once you are back at the bottom of the descending reservoir footpath, continue straight on to take the high route back to the car park. Beautiful views of the narrow valley and the impressive dam wall.