We propose to use an array of MEMS gravimeters delivered by any of several methods to generate high resolution maps of underground facilities and construction activities. This is accomplished by measuring the strength of the Earth’s gravitational field at interesting locations with extraordinary precision. With three dimensional gravitational field strength measurement afforded by using an array of MEMS gravimeters, the effect is anticipated to be similar to the volumetric visualization of anatomical structures in the medical imaging industry through passive imaging techniques. Detected anomalies would be marked for further measurement; multiple overflights of suspected underground facilities would exponentially increase the resolution of the generated underground map. Delivery methods at the present time are: (1) special briefcase carried near the facility, (2) drone flights near the facility, (3) cluster bomb of probes that fall through the air near the facility, and (4) disguised objects and buried sensors. The same system in a mobile configuration could be used as a GPS alternative by permitting gravitational navigation against a stored map, without relying on satellites.