I've done this walk a few times. Normally we would get dropped off close to the start of the walk in Kenmare and then walk to Killarney, finishing at Muckross House, or Torc waterfall. It's a really nice walk away from the traffic.
Lush vegetation, and interesting Ricky rugged hills. You drive through a very old tunnel, as shown here on the photo. Nice place for a scenic drive.
This drive is gorgeous but be aware that roads are very narrow and there is a ton of tour bus travel in this road! If you meet them coming the opposite direction, it can be a super tight squeeze but well worth the added stress!
If your driving this is a fun drive to take the scenery is outstanding and there places to stop and walk down to the lakes and couple of places to stop for coffee.
Probably, one of the best drives in Ireland is the Killarney - Muckross House - Old Kenmare Road - Molls Gap - Blackwater Valley - Gap of Dunloe - Kate Kearney's Cottage - Killarney. Takes about 2-3 hours with great stop offs (Muckross House, Molls Gap, Ladies View, Kate Kearney's Cottage). Essential tick list for any Killarney trip.