100:00:01,000 --> 00:00:03,601NARRATOR:Enormous man-made caves.200:00:03,635 --> 00:00:04,902PAUL BAHN:Nobody knows what on earth300:00:04,936 --> 00:00:06,872these things are.400:00:06,904 --> 00:00:08,874NARRATOR:Unexplainable structures.500:00:08,906 --> 00:00:11,509LOGAN HAWKES: You ask them,"How did you build these?"6