read at Google Earth Blog
Google has added a new layer tonight. The layer is for the 'Museo Nacional del Prado' in Madrid, Spain. This layer is special because it shows you a selection of 14 paintings from the museum which have been scanned at ultra-high resolution. You use the Google Earth Photo Overlay feature to view the paintings. First, you can find the new layer in the Layers pane under: 'Geographic Web -> Preview -> Museo de Prado'. Once there, select the layer (if it isn't already) and double-click the 'Museo Prado' placemark. This will fly you to the museum. Make sure the '3D Buildings' layer is turned on to see the outside of the museum rendered in 3D. Then select the placemark 'Museo Nacional del Prado' and you should see 14 thumbnails of the paintings Google selected for showing (they said it was hard narrowing the choice to so few, but these are among the best)."