We travelled the Causeway Coastal Route from Bushmills to Ballycastle and found the scenery beautiful and the drive pleasant. We stopped at the Causeway, White Park Bay, Dunseverick Castle, Carrick-A-Rede and a few miscellaneous laybys.
We stopped at the Dunseverick Castle ruin as we made our way along the costal route. There isn’t much left, but what there is on its outcropping is impressive. The surrounding views are also great. There is a National Trust carpark on the causeway side of the ruin, and a layby/viewing area on the eastern side. Both parking options are free.
Several of these have viewing spots where payment isn’t needed, though Causeway and Carrick-A-Rede are major National Trust sites and have paid parking (unless member). The views are worth the drive and it is a great alternative route to using the motorway back down south.