why not find the locality .. using a stethoscope .. and start to dig down ....! If your saying its like ten feet below your feet - then that shouldnt be too hard to dig down to .. and you may find yourself ... opening a hole in a military tunnel ... !

That would be fun to investigate - they aint gonna see you coming through the roof their tunnel and having a look round ..! Man you could maybe even get some listenning devices down there etc etc ..


regards
JF