article_snippet.sent: a systematic study of a 1.5 mile (4 km) area using geophysical resistivity and seismic tomography suggest the underground corridors may go as deep as 371ft (113 metres), but the exact size remains unknown.
article_snippet.sent: a systematic study of a 1.5 mile (4 km) area using geophysical resistivity and seismic tomography suggest the underground corridors may go as deep as 371ft (113 metres), but the exact size remains unknown .
highlights_snippet.sent: Study suggests underground corridors may be 371ft (113 metres) deep .