Ireland to Scotland and Back (also can you park a rental car for 3 days?)

Key question - where in Scotland is your friend? Actually in Edinburgh or elsewhere in Scotland?

Yes you can park, for a fee, at Belfast port. BUT what's the point to paying for a rental car to be sat at Belfast for several days, then having a 3 to 4 hour journey each way on transit from Cairnryan to Edinburgh.

From Belfast City Aer Lingus fly to Edinburgh, and from Belfast International both Easyjet and Ryanair. From Dublin there are lots of low cost fights on Aer Lingus and Ryanair.

Belfast City to EDI £59 each way next May on Aer Lingus, Easyjet from Belfast International typically £29 each way, Ryanair typically 27 to 30 Euro out of either airport, so lots of low cost options.

The one-way international drop charge between the Republic and NI can be pretty punishing so you'll want to ensure that you return your rental car in the same country that you initially rented it from.
You neither need nor do you want a car in Dublin or Belfast - just too much of a hassle. Better (I think) to return the vehicle in one city or the other once you've finished touring the countryside and be done with it. Then catch your cheap flight over to Scotland and arrange the last portion of your itinerary so that you finish with a few days in Dublin ... both car and carefree ... before your flight home.

Please share your itinerary in Ireland. We really can't offer good advice with little information. Are you going to be in Ireland or Northern Ireland? Do you really need a rental car for your entire time? (And I agree that parking a rental car for three days is a waste of money--both the cost of the car rental and the parking fees.)

There are plenty of flights between Dublin/Belfast and Edinburgh. But is Edinburgh the closest airport to your friend?

Did you look at buying one way tickets instead of open jaw tickets. Open jaw is flying into one airport and home from another and usually is not that much more expensive . We flew from.Philadelphia to Edinburgh and home from.Paris and flights were not expensive. I just looked up flight from Boston to Dublin and home.from Edinburgh to Boston and cost was $673 for lowest cost and one way Boston to Dublin was $703 for an example.

Return your car at Dublin Airport and fly to Edinburgh and back, in time to connect with your homebound flight from Dublin. Northern Ireland may be part of your driving plan, but returning the car at DUB will save dropoff fees. Whatever time you have for Dublin itself should be either at the start of your trip, between returning the car and flying to Scotland, or after returning from Scotland and before returning home. You won't want a car in Dublin itself.

I will be picking up an Avis Car Rental at Heathrow airport in June 2024, then driving to Holyhead Whales and taking the Ferry to Dublin Ireland, At this point I will be driving to Belfast Northern Ireland. I will then drive to Lame Northern Ireland and take the Ferry to Cairnryan Scotland and return this rental Car a week later to Edinburg Airport. Is this usage of an UK Rental Car legal & what extra Documentation or Licenses are needed to accomplish this task Please?

@ dave-schafer- this would be much better as a separate thread- as this is quite a big question, which deserves it's own thread for reference. Also that way you will get notifications of all responses.