Sarah, this is a bit of a tricky one, but I'll do my best. Most of my recommendations are coming from outside sources, but just so you can have somewhere to start your own search... here we go!

First, Ireland is not a huge country. You could rent a car and drive a few hours to another part of the country to see castles, in fact I'd recommend it. Car rentals are very affordable in Europe!

That said, I feel like you could easily drive (< 3 hours each way to these places) to some of the places on this list:

1. Dromoland Castle Hotel in County Clare will give you a beautiful perspective on West Ireland, and will also give you an easy striking off point to the Cliffs of Moher (one of my top 10 places in the world to visit!). While near the cliffs, be sure to have a meal at Vaughans Anchor Inn... my favorite seafood meal of all time.
   
2. Ashford Castle will take you a bit farther north in the west, and I hear that part of the country has a bit of a more distinct feel than the rest of the emerald isle.
   
3. You simply must go to Blarney Castle, even if you can't stay in the castle... Cork, and the south part of Ireland, are breathtaking, and if you can swing it, I'd stay in Kinsale for the night. Dinner at Fishy Fishy Café was one of my best meals!
4. Swords Castle is apparently very charming, and recently featured in The Tudors, if that's your sort of thing.
   
5. Fitzpatrick Castle Hotel is another one that looks to be pretty reasonably priced and very near Dublin. 

I hope this helps your planning! If you have the time, I'd definitely opt for the out-in-the-country experience along with Dublin. Ireland is very charming (as you can tell from my answers), and Dublin is just one small part of that!

Sources: 

• http://www.cntraveler.com/daily-traveler/2012/04/castle-hotels-england-ireland-germany
  
• http://www.exploring-castles.com/castles_in_dublin.html

Trim's Trim Castle is one of the largest Anglo Norman castles in Europe and is one hour drive from city centre. It is very impressive, has a good tour but you cannot stay overnight in it.

There are a lot of castles in Ireland!  If you're going to be in Dublin, then Dublin Castle in the heart of the city is a must see (the Queen and Barack Obama have both visited there recently).  

Kilkenny Castle is another stunner of a castle which can be visited on a day trip from Dublin, but if you have time, I'd advise an overnight stay in the medieval city of Kilkenny - great food, traditional pubs and full of history. If you want to stay in a castle, then check-out this website: http://www.irishlandmark.com/.  They rent out restored historic properties and you can stay in anything from a castle, to a gate lodge, to a light house.

Another vote for Trim Castle, great tour. I also liked Cahir Castle and if you visit there you must also take a walk out along the river to The Swiss Cottage. 

If you want to get off the beaten track a bit Drimnagh Castle is a nice spot to visit. The day I went I had the guide all to myself and he must have spent nearly two hours chatting to me. All for €4! 

If you are going to see a lot of heritage spots while you're in the country consider getting a heritage card. 

http://www.heritageireland.ie/en/Info/HeritageCards/

Ashford Castle is outstanding place to visit and stay -highly recommend.  But not many 'good' ones nearby Dublin.....most are 2+ hrs drive by car.....I lived in Dublin for ~1 yr and that was one of the worst parts.....all the really NICE parts of Ireland are on other parts of the Island!

Hey Sarah,

Right in the middle of the city is Dublin Castle which is steeped in history and was home to the British pre-revolution - beautiful gardens there too out back.

Then a 20 train ride north via the DART (train) from Tara Street Train Station is Malahide, a lovely coastal town with a great caste to explore.

Finally there is Clontarf Castle Hotel just on the outskirts of the city where you can stay (it is now a hotel). 

Beyond Dublin you should also explore Glendalough in bordering county Wicklow where there is a monastic site dating back to 600AD and beautiful lakes to walk around - you can jump on a tour bus to get there, about 1 hour south of Dublin.

Check out likewhere.com for where you should go in Dublin based on what you like in Seattle!

Have a great trip!

-Simon.

HI Valerie, Allow me introduce you to our complete range of Castles to visit, to stay and to engage with through our range Attractions, Immersive cultural experiences and Festivals and Events all over Ireland see www.discoverireland.ie  and search ... the choices are endless! We look forward to welcoming you