seebyf,

I don't know of any tours that combine Newgrange and the Giant's Causeway. You can do Newgrange as a separate day trip, returning to Dublin at the end of the day. You can do the Giant's Causeway from Belfast or from Dublin; again as a separate trip. If you can rent a car that will make best use of your time and you can combine the various sights instead of doing them piecemeal. If there is more than one person, it may just be worthwhile renting the car. Let me know if you want the links for the tours.

The Antrim Coast is spectacular. There are hiking trails along the coast if that sort of thing interests you. Otherwise, I would just explore all the beaches and bays, Carrick-a-Rede Rope Bridge, Giant's Causeway, Dunluce Castle, Bushmill's Distillery, Toor Head Drive. For lodgings try Craig Park near Bushmills or Crockatinny near Ballycastle. You would need a car to access them.

Michele