For all practical intent and impact, there is NO border. It is about as seemless as crossing a State Line, in the USA.
They use GBP (Sterling) in N.I. and all speed limits and destination signs are in mile, versus the Euro and kilometers in the Republic.
The only caveat: Car rental insurance is cheaper and easier, using a credit card, if originating and completing in N.I., since it is part of Great Britain, but that doesn't seem to apply to your situation. You'll probably have to pay a N.I. fee to the rental company because you are taking the car into N.I. (about 35 Euro, last summer).
Watch out for a SUBSTANTIAL drop off fee on that rental, too. Enough that it MIGHT be cheaper (or as cheap) to drive down to Dublin, spend the night, drop off the car and fly home from there.
Bob
Bob
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Bob
Help Us to Help You. The more you tell us about your plans (dates, interests, budget), the better we can tailor our advice to suit!
Our original thoughts were to fly into Shannon and out of Dublin, but I was afraid that the extra distance back down to Dublin might be pushing things a bit much.
We will arriving on 4/24 and will be leaving on either 5/9 or 10. The places we would want to visit are Galway, Sligo, Donegal, Letterkenny (I have a client to meet there), Giants Causway, Belfast.
Another option I was thinking was to fly in and out of Belfast, and just do Northern Ireland, Do Donegal and Co Sligo, but I wasn't sure if there is enough to see and do to fill our time.
We did that trip in September, Burren, Galway, Mayo, Sligo, Donegal, NI, Dublin. As Bob has said we didn't notice anything different except the money and the speed limit signs. We rented our car from Dan Dooley and didn't pay extra to take it into NI (and I did specify that when I booked). We dropped the car off in Dublin and also didn't pay a drop off fee. If you do this trip, you will love Donegal and NI. I have a trip report in the works on the Trip Report section. The only part of the trip not covered so far is Dublin.
Bob & Merle were just recently in No. Ireland. As they said the border crossing is not noticible. No more soldiers with machine guns!
I would have no problem filling two weeks with things to do in No. Ireland, Donegal and Sligo. There is so much to see and do if you just scratch the surface. The drive from Belfast to Dublin takes about 2 hours. There is a very good highway between the two starting near Newry. That may give you a point of reference for planning your trip.
Check on the different car rental companies. All have their own rules. Some have an extra charge to go into NI from the Republic, while others don't. All that I have checked have a drop-off charge when renting in the Republic and dropping in NI. The reason being they have to shuttle the car with the Republic license plates back to where it came from.
The only problem with the time you are traveling is that many things in NI are only open on weekends. Take that into account when planning.