An obvious place to start from is the car park at O261 259 A from which paths will take you south the 400m or so to the summit. Huge numbers of people come here often with dogs. Sometimes at busy times the car park can overflow.
At the top there is a large monument and a great view of the coastline and the nearer peaks of Dublin and Wicklow such as Djouce. Sometimes the coast of Wales can be seen from here, such as Yr Eifl on the Lleyn Peninsula.
From the summit the slightly lower Dalkey Hill can be reached to the NE. This is above Dalkey Quarry, famous for rock-climbing.
Killiney Hill and the distinctive monument on it can be seen from much of south Dublin and the north eastern corner of the Dublin/ Wicklow Mountains. Linkback: https://mountainviews.ie/summit/1346/comment/15590/

A very pleasant 10-minute stroll from the Killiney Hill car park along pathways that weave through mature woodlands, takes you to the high point of the hill, marked by a large obelisk and a couple of other odd follies - but on a fine day the views are quite spectacular, with Dublin Bay curving round to the south, presenting an aspect of the Dublin/Wicklow mountains with Killiney strand stretching out below, and this time of year the hillside is covered with masses of yellow furze. It's easy to understand why many of the roads around Killiney/Dalkey have Italian names like Sorrento and Vico, because the view is very reminiscent of the Bay of Naples, although I'd argue even better! Luckily, the Sugar Loaf, unlike Vesuvius, is extinct. Linkback: https://mountainviews.ie/summit/1346/comment/17968/

Surely the greatest reward for the least effort, especially on a fine spring day when the wildflowers are in bloom. The views of Dublin Bay are tremendous, and the masses of furze and red valerian make it simply majestic. Up and down in 40 minutes, although you'll probably want to linger for a lot longer at the top. Linkback: https://mountainviews.ie/summit/1346/comment/23509/

A simple walk around a hill with trails with great views out over Killiney Bay. The car park mentioned by simon3 is the obvious starting point. Linkback: https://mountainviews.ie/summit/1346/comment/20149/