Climbed Knockbrack and Dromderalough on 13/11/05 which was a bright but cold day.
The minor road on the right is on the Kenmare side of Kilgarvan, just after the sign for the GAA grounds but before the Michael J Quill Memorial Centre. There is a right turn roadsign about 100m before the minor road.
As it was such a fine day, I decided to park just south of Mangerton Bridge at V995762 B using a good layby on the right. I then followed the road north, then west to the last farm at the end on my right. Here, you will see the rather intimidating Private Property signs as mentioned by mat in his comments on Dromderalough. I counted 3 of these signs, but a 4x4 vehicle passed me at the entrance to the forest and I was not challenged.
I would suggest following the route up Knockbrack as described by Grumbler#1 in his comments on this mountain. Paddy Dillon in his book The Mountains of Ireland suggests leaving the track at the forest entrance and following the forest boundary fence in a north-westerly direction. Staying on the forest track is an easier option, although perhaps slightly further. Look out for the sheep fence on the final approach to Knockbrack, complete with a barbed-wire top. Views from the top are good, with the Reeks, Stumpa Duloigh and Mullaghanattin all prominent. I encountered a small group of red deer just north of the summit on the way to Dromderalough.
Dromderalough appears to have 3 separate summits, all marked by cairns. I continued on to Mangerton, which involves crossing some very rough and wet bog. This was hard going, and adds around 2 hours to the walk if you return to Dromderalough from Mangerton. On top of Mangerton, there was a group of at least 30 school children. On returning to Dromderalough, I descended south-easterly across open hillside to return to the entrance to the forest. Here, you can rejoin the forest track next to some sheep pens. As I walked past the last farm on the way out, I met the farmer. He told me the signs had been put there by the company (South West Forestry) which manages the forest. Parking in the forest is possible, but may not be a good idea in view of the private property signs. The road walk to and from Mangerton Bridge adds around 4km in total, but serves as a good warm up/warm down. Parking here is also not obstructive in any way.
Knockbrack and Dromderalough may not be the most spectacular hills in the area, but are well worth the effort. Linkback: https://mountainviews.ie/summit/255/comment/2055/

Some mountains, like Errigal, are great because of their aesthetic beauty, others are great because of their technical difficulty. Knockbrack is neither. Nevertheless, this was a great day, and this small bump will be remembered by the other Grumblers when we have forgotten bigger hills.
Grumbler #2 (aka "Trip" ...a great nickname for a climber!) and myself had a little race going on. Who would be first to finish all the 2000ft peaks in Ireland? Trip had one left.....Knockbrack, he'd missed it when on Mangerton, as the OSI don't give a spot height). So we had to make a weekend of it, Big Jock came over from Glasgow but his brother "Mad Jock" had just secured a job and sent an apology in the form of a bottle. Being a special weekend, various honorary Grumblers also came along and a plan was formed. Day 1 Galtees, Day 2 The pocket, Day 3 Whatever, Day 4 Knockbrack. Day 1 was torrential and cold as winter (it was only May after all), Day 2 started gloriously but we were denied access to Mullaghnattin from the South by an irate farmer (tip: don't ask permission) I'll post the Ballachabeema route epic soon. Day 3 being Sunday meant Knocknadobar via the stations, followed by too many pints in the Roughty bar in Kenmare (and not enough elsewhere).

So the big day dawned, totally hungover and dehydrated. The biggest navigation problem was finding Mangerton Bridge (995762 B) and the road below Carrigagreenaun. Parked at the end of the road taking care not to block the new sheep pens. Keeping to the right (and then turning right) on the forestry track, plodded gradually uphill with a head thumping like drum. Track swung left (W) again and zig-zagged up to the end of the forestry as the clouds and our heads cleared. The track dropped us by a fence and a stiff 150m or so pull NW saw most of us on the top. Trip was with the "auld wans" so big Jock ran around the 4 bumps with his GPS to let us know that the "wee cairn" we stood by was the summit. True baggers will need to satisfy themselves and do all 4 peat hags, Good views though. Finally grumbler #2 reached the top. (Sensitive souls and puritanical sorts stop reading now) Whiskey was produced, of the Scottish Malt variety. Lots, and by god it was marvellous! Photos were taken, hands shaken, I admitted defeat. The conversation began "Perhaps the 600m tops? or highest point in each county?" "Whats the highest point in Kildare...the bar stool in The Kitchen...." We continued on elated to Dromderalough for more traditional food and drink and shelter from a passing shower and discussions, lists, and thoughts of new routes on proper mountains. Looked at Glencappul SE Top, the Grumblers Executive (me) decided that it was dubious to accord it separate status to Mangerton, while Big Jock laughed (no doubt the SMC has a special committee and teams of surveyors for such things). Dropped S, down the least boggy gully to reach the Owbaun river and a track by a fence. At the end we kept left (E) to avoid walking by the farmhouse, to regain the road. A quick trot up the road, a wash in the stream and back home.
Thoughts from the barstool in "The Kitchen": If you want an easy day at the end of a weekend's walking, to stretch your legs, or can not face the drive back to the Pale, you could do worse than this. Linkback: https://mountainviews.ie/summit/255/comment/595/

Climbed Knockbrack on the 08/03/2009, from a different side to those in other comments. Left car at Gowlane Cross (91751), about 2 miles from Kenmare town (past the Church and schools and straight on), and walked north east along the tarred road. After approximately half a mile, there is a large newly build shed just off the tarred road on the left hand side (924758 C) with a gate in front which is just closed by a wire. I left the tarred road and went through the gate, past the shed and up a track that leads from behind the shed along by the base of Knockaganuish Mountain on the left (West) wide and on to Cummerslaun Lake. Near the lake a river crosses over the track, and at this point (925774 D) I turned off the track and followed the river back to its source, Lough Nambrackdarrig, which is in the valley between Knockrower, Dromdiralough and Knockrower. Going wasn't easy as weather was very bad, snowing and windy, but terrain was fine - though should bear in mind that the north side of the river has a track carved by quad bikes and there are few natural fording points in the river during rain. When I got to the lake, (944783 E) I headed south east across about 50 yards of very boggy ground towards a very distinct rock on the west side of Knockrower which is clearly visible against the sky, and from there made my way east to the summit. Some rocks and boulders, and one set of crags about half way up and which are easy enough to get around, but otherwise no real obstacles. The top is not very clealy defined, no cairn, so its a bit of guessing and sizing one outcrop of rock against another. In wandering around the top I found the two lakes marked in all maps near the top, on the day I was there one was all but frozen over. Some spectacular scenery from the summit, though the conditions were alpine with snow and a strong gale which almost bowled me over a few times. No big cliffs though, pretty safe there. Walked down pretty much the same route, though this time circled Lough Nambrackdarrig to the east and north before finding the river again and following it back to Cummerslaun. Overall it took about 4 hours, though stopped a lot to take photos. Linkback: https://mountainviews.ie/summit/255/comment/3635/

As an interesting detour, and for a fun scramble down a steep incline, if one walks from Knockbrack east south east towards Knockanganuish, staying to the south of the valley through which the river from Lough Nambrackdarrig runs (is this the Ullauns River? Think it's noted as such in McGonigle's Guide to the Killarney outback) there is a ridge which leads to an area containing forestry. When you find the forestry at V935773 F turn south and follow its north east boundary. After about 10 minutes walk (maybe 25 mins from Knockrower summit) you will find a stream beside an area of forestry that looks like it was burned in recent years. Stay as close to that stream as possible, even though the going can be sticky and boggy - it becomes a spectacular waterfall dropping about 100m through the forestry, and great fun can be had scrambling down beside it. Rocks in it are very slippy though, so take care or you'll end up on your seat. At the bottom, there is a path which takes you back to a track at at V925770 G, and eventually back to a tarred road near the Old Killarney Road. Linkback: https://mountainviews.ie/summit/255/comment/3741/