Itinerary Advice 12 days in Ireland

I think this sounds like a great trip! And will definitely allow you to get some beautiful hiking in.
If you have not already picked an accommodation for Doolin, I'd suggest looking at Sheedy's (https://sheedysdoolin.com/). You can walk to the Cliff's trail from the BnB or in to the old town or new town. It is hands-down the nicest BnB we've ever visited. And the breakfasts were outstanding.

Thanks so much for your input. Will check out the hotel, but things are really booked up over there!!!

Why would you not get the car before going to Glendalough? You're backtracking by returning to Dublin that night.

We don’t want to drive in Dublin.

So you do know that there's no train station in Glendalough, yes? The closest station is Rathdrum and from there you would need to take a taxi. You'll also want to make arrangements for the return to the train station. There's no "taxi rank" at the monastic site.

y 4: Taxi to car pick up in Dún Laoghaire.
This is where we r picking up the car. The day after we hike in Glendalough. Dun Laoghaire is in south Dublin, out of the city center as I understand it.

Most of your trip looks great - not too rushed.

On Day 3, have you thought about picking up your car at Dun Laoghaire and driving on to Glendalough, then staying nearby? I ask because right now I am at a nice bed and breakfast a 4 minute drive or a 25 min walk from the Visitor’s Center.

While that doesn’t really change your driving time on Day 4, it would definitely save you from returning to Dublin on Day 3 and then doubling back on Day 4, not to mention the question of getting to and from Glendalough, and might allow you some evening hiking if you are coming in summer when days are long.

That might work if there is public transportation from Dun Laoghaire to Glendalough. Or a short taxi ride. What is the name of the b&b that you are staying at? Thank you !

Are you staying in Dublin or Dun Laogharie? If you're staying in Dublin it doesn't make sense to rent a car in Dun Laogharie in order to drive to the Rock of Cashel. You'll have to get on the M50 ring road which can be an absolute nightmare during rush hour. You would be better off renting from one of the agencies on the South Circular Road in Dublin. From there it's an easy shot to the N7 and then the M7 and M8 to Cashel. If you can find accommodation in or near Glendalough then renting in Dun Laoghairie makes more sense.

Just go ahead and rent your car in Dun Laoghaire like you planned, but do it on Day 3 instead of Day 4. Then drive to Glendalough from Dun Laoghaire and spend the day, staying nearby. On Day 4 get up and leave for Cashel and then Kenmare. Then the only transportation you need is Dublin to the car rental place.

I am staying at the Tudor Lodge B&B.

Thank you both. I am just trying to mitigate heavy traffic, considering it is the first time my husband will be driving on the left hand side of the road. We are both a little nervous about that. I will look into that B&B that you have recommended. Many thanks to all