​The walk is a simple 24.5km loop all inside Glenveagh National Park. The entrance is free of charge.
The route is made of an easy part and a second one more strenuous. It starts from the car park at the main entrance. Just follow the path along Lough Veagh and continue straight to the gap. Near the gap, you can see a well marked path on the opposite slope, veer to this path and follow it nearly 700m. If it is opened, you can reach it lower in the valley (hundreds meters before point A, blue flag). Do not forget to look at behind you sometimes for the beautiful view on the valley.
After these easy 11km, the "hard" things begin. Follow the path until it disappears near a stream, continue your route to the north through a marshy ground. You can climb Crockmulroney (430m) and Cro an Lochain (486m) for a last view on the valley. When you reach Loch na bhFaoileog, the small lake with an island, you have the choice to reach Cruach na Sagart (480m) and to follow the smooth ridge or you can walk directly toward Dooish summit (652m). Whatever your choice, you will have to negociate with eroded turf. A grassy straight "corridor" may help you to find your way on the steep slope to the north (point B, red flag). From here, I saw nearly sixty deers until I reached Dooish. Once you are on the summit, follow a straight north-east route until the car park.

Warning : pay attention to the ground with hidden cracks, unstable tufts of grass and a marshy soil. To make your own opinion about the difficulty, I walked the first part (11km) in 2h11 and the second one (13.5km) took me 4h56, stops included. GPS signal may be weak or null.
Nota : this walk can be done in a nicer way if you do it in counter clockwise. You will then enjoy the valley an Lough Veagh along your return path. Furthermore, you have the opportunity to have a tea at the Castle and for few euros, you can avoid the last 4km by bus if needed.