The approach to Slieve League is quite an experience before even start walking, the road twists and turns, with big unprotected drops down into the Atlantic below. The carpark (557757 E) gives a fantastic vista of the steep high sea cliffs and the walk to come, with great views out over Donegal Bay.
There is a good path from the carpark and its informative information board, along stone steps and easy grass - this soon changes though and the track becomes quite heavily eroded through areas of peat and rock (a testament to the heavy traffic the hill no doubt attracts). There are breath taking views along the lenghth of the sea cliffs to Rathlin O Birne island. Soon come to a series of little jagged tops which contain the rib of rock already mentioned in other comments - I climbed up to its start but the steady breeze told me it was not a good idea to attempt and the easier track below won out. Ever higher vantage points have the hand reaching for the camera - be prepared for numerous stops to take pictures. After 1 hr 10 minutes i reached a large cairn and a level area at the summit. Continue along the cliff edge - looking back over the cliffs to the now distant carpark. There are cracking views to the Sligo Hills, along the Ox mtns to Nephin and then Corribinnia and Glencar in the Nephin Begs and to lands end at Belmullet. There are also good views N to the Derryveaghs and the Bluestacks.
There are a number of cairns as travel easily along the cliff top before drop down and cross One Mans Pass - the narrow ridge leading to the true summit area - not really anything too worry about unless the wind was howling. The summit area has a "sawn off" trig pillar and a couple of small cairns, with views over to Leahan Mtn (427 m), Rathlin O Birne island with its lighthouse and N to the signal tower and the jagged top of Sturral Head further around this magnificent coastline. The E breeze was whipping down the cliffs and creating spreading patterns on the ocean below - a solitary fishing boat the only other disturbance.
Return back along One Mans Pass to the first large cairn encountered on the climb, i noticed a perfect little igloo shelter built here. Take the E running spur above Lough Agh. there appears to have been some sort of competition here as i counted over 20 sizeable cairns. The going is very good on grass and small stones, with great views down over Lough Agh and across to the slopes which end abruptly at the huge sea cliffs. After reaching a cairn there is a drop down and a small rise to the top of Lergadaghtan Mtn (5666784) - from here it is a steep drop down towards sheep pens and the Old Mans track. Follow the track to the road and turn L uphill, this joins the road to Bunglass, turn R and are back at the carpark after 50 minutes of road walking. Absolutely fantastic days walking and as was during the week there were only a few cars in the carpark. It is worthwhile heading down to the signal tower at 563748 F. Linkback: https://mountainviews.ie/summit/285/comment/2289/