to continue on the industrious way, i'd like to suggest seismology surveys.
such research is used to determine the composition of the soil.
In this case it would tell the locations of underground lava lakes, and caves/caver
ns and such.
this to facilitate geothermal energy production
i would see it working with a few components.
a central processing apparatus that records .
some sensors that transmit the data to the recorder;
craft some explosive charges, not tnt, to generate sound or 'thumpers' ala 'dune'.
results of the survey yields some data, so repeated surveys are needed to refine the map.
extra's:
some gadgetry like messages that the thumpers are registring with the recorder.
possibilities to make printouts of a certain level that you can navigate.
crosssection survey results, showing you what is below you.