Although there's nothing comparable—in my case, to the point of getting goosebumps—to standing in front of Las Meninas (or any of the Velazquez masterpieces, for that matter), the dark Goyas, or the Fusilamientos del Tres de Mayo, this is the closest you can get to them from anywhere in the world. In fact, you can get closerer and closerer than in front of the real thing, unless you want some Prado staff goon to hit you on the legs with a taser.
The amazing images are 14 gigapixels, 1,400 times the resolution of a 10 megapixel camera. As you can see in this video, Madpixel doesn't use any special camera, but a machine-controlled digital camera and algorithms to compensate for deformation and stitch the final result. Zooming in to see the masters' technique and the detail in the painting is just mindblowing.
[See it here (requires Google Earth) via Madpixel]