What lies beneath the Moon's surface ? The openings, which were found near the Moon's north pole, could lead to an extensive network of tunnels. Discovered by researchers working with the SETI Institute and Mars Institute, the holes, which were spotted on photographs taken by NASA's Lunar Reconnaissance Orbiter, are thought to lead down in to a network of ancient lava tubes which carried flows of molten rock in the Moon's distant past. It remains unclear exactly how deep the holes go or how extensive the tunnel network might be. "The highest resolution images available for Philolaus Crater do not allow the pits to be identified as lava tube skylights with 100 percent certainty, but we are looking at good candidates considering simultaneously their size, shape, lighting conditions and geologic setting," said scientist Pascal Lee. If the holes really do lead down in to tunnels, these subterranean caverns would be an ideal place for future human explorers to shelter, set up a base and