Kilkenny Castle Gallery
This gallery in Kilkenny Castle is really quite stunning to walk into, and there are photos of it from early last century showing the walls absolutely covered in artworks - as was the fashion at the time. Now the paintings are laid out in a compromise to a more modern sparseness, but the walls are still richly coloured rather than white.
The decorative details are also impressive, and I've included a detailed picture showing the painted ceiling from the far end (the whole ceiling is extensively decorated).
All well worth the €7 entrance fee.