In reply to TobyA:
I can confirm that there are no covid related issues crossing the border and that you will not come across any checks. As JB says, Covid rates are about 3 times higher in Northern Ireland than Republic but of course this is subject to change. Most car hire companies in Northern Ireland do not charge extra to drive in the Republic of Ireland but do ask at the counter.
Try:
Slieve Gullion Park, Dunluce Castle, Strangford Lough, Ferry to Greenore to visit The Cooleys and Carlingford Village, Antrim Glens, Lough Erne (Boa Island), Derry (City Walls Circuit), Rathlin Island, Giants Causeway (Very early/late) and Fair Head, Mourne Mountains (Carrick Little, Meelmore Lodge or Hen/Cock Mountain access areas), Carrickfergus Castle, W5 and Titanic (kids wet day in Belfast).
Just a few ideas and do enjoy the holliers!.
Post edited at 03:00