The event display from the NOvA Far Detector. This image is live data.
The top large rectangle is the view from above, the bottom the view from the side. The NuMI beam from Fermilab is coming in from the right of the picture. Each pixel in these views is one long (15.6m), thin (4x6cm) PVC cell filled with mineral oil.
A "lit" pixel is one where a charged particle crossed that cell, making a flash of light.