I have two suggestions. Either drive with the intention of visiting the ancient monastic settlement of Clonmacnoise or Birr Castle. (You could do both, but possibly best to concentrate on one)
My favourite of the two is Clonmacnoise, However you should google both these places and decide if they would interest you. Both are approximately half way between Galway City and Kilkenny, so good stopping places to stretch the legs and have lunch/snack. There are cafes at both sites.
Note that you cannot tour Birr Castle itself as it is still a family home, but its famous observatory and gardens are open to the public.
At Clonmacnoise the entrance fee includes a guided walking tour if you want that (and I recommend it) and a short explanatory film is also offered.
Either way both of these sights are a very short detour off your route from Galway to KilkennyEdited: 12 August 2017, 02:07
Clonmacnoise and Birr are both good visits, both very close along the way. Clonmac in the morning then lunch in Birr, maybe? Birr also has an interesting exhibition on and connection with the Parsons family who a) owned it and b) were responsible for inventing turbine engines, if that helps to float your boat.