Madrid's Museo del Prado has made ultra-zoomable "gigapixel" scans of fourteen of their masterpeaces, including Velazquez's Las Meninas, Goya's Third of May, and Bosch's Garden of Earthly Delights, available through the Google Earth application. In truth it seems like a bit of clunky way to gain access (open Google Earth, zoom in on Madrid, find the museum), but once you're in you can zoom and pan across every crack and brushstroke. I loved this close-up of José de Ribera's surprisingly naturalistic 1639 depiction of Jacob's dream at Bethel, in which he saw the angels of God ascending and descending on what I always pictured as a sort of celestial shopping-mall escalator. But here we only see the face in repose.