Kilkenny Castle is the type of castle you picture in your mind. Imposing from the outside, opening to a great park at the rear and a garden with fountains at the front. Kilkenny Castle is almost like a fairy tale.
Kilkenny Castle belonged to the Butler family, the earls of Ormande from 1391 to 1967 when it was handed over to the Irish government to be painstakingly restored to its former splendor. Guided tours through the castle are available; arrive early and book ahead if you can to avoid disappointment (or naptime).
Note: Kilkenny Castle is an OPW Heritage Site. You can purchase an OPW card here for use at other OPW sites. OPW cards are good for one year from purchase.
The restoration of the castle is breathtaking; it has been refurnished with period pieces and portraits of the Butler family )as well as a King and Queen of England) and a suite of Brussles tapestries. Unfortunately no photos are allowed inside so I strongly suggest a short stop in the bookstore to pick up a visitor's guide and a few postcards.
If you don't plan ahead for a tour (because we didn't- learn from me) be sure to take in the grounds. The entrance to the grounds is through the arched gateway in the curtain wall along the Parade. (Before you enter look to the right. See if you can spot the garedrobe (toilet) chute and small Posturn Gate with stone steps that led to the moat.) This brings you into the courtyard; you are surrounded on three sides by the castle.
And laying to the east are acres of parkland. If it's sunny stop and pick up some Irish cheese and some bread for a picnic on the grounds. Bring a ball or kite. This is a perfect spot to relax and play. In fact, there is a play area for the kids with swings, climbing areas and slides.
To the west of the castle (accessible by walking around the castle or through a gate from the Parade) are the formal gardens. Obviously they are much more beautiful during the spring and summer but the girls were fascinated by the fountain.
The River Nore runs along side Kilkenny Castle and a river walk is accessible from the park.
While there are other great things to do in Kilkenney I recommend heading just south of town to the Medieval Kells Priory. Heading south on N76 from Kilkenny follow signs for r699/Callan and stay on R699 until you see signs for Kells.