Muons, generated by the collision of solar wind with the upper atmosphere, were used forty years ago to examine the inside of the Great Pyramid of Egypt. Highly directional detectors were placed around the pyramid and a 3-D image generated similar to a CAT scan. The same technique has recently been proposed to see what is under a Mayan temple:
http://www.sciencenews.org/view/feature/id/9179/title/Muons_Meet_the_Maya
How far are we from realizing the "Star Trek" technology of visualizing the inside of a stucture using a "sensor array" of directional muon detectors?