Henry wrote to Marie - "Last Saturday Esp explored a cave - the largest in Mexico, known since 1650. Cave is huge but only 3.5 miles long - there the underground river disappears thru narrow low tunnel like gorge. No one had ever gone beyond. Esp and 8 men in swimming suits, equipment on back entered the river there. She went 1st, passed thru tunnel and signalled back to others. They took wonderful photos, travelled 16 hours, rested 3, were underground 19 hours in cold, wet bathing suits. no sleep, no food. Travelled about 25 miles."