farida, who performs cesareans on wounded women, and her husband, dr. abdulkhalek, an eye surgeon. >> dr. abdulkhalek: they couldn't destroy this building, so, they used a chemical weapon. in the last two days of the siege, we noticed the smell of chlorine. and we rushed all of the staff, all the patients, to the inner room in that basement. and during this time, many children came to our hospital, and we had just one remaining bottle of oxygen. so, we had to transfer the mask between the children, one small amount of oxygen for each other. ( shouting ) ( crying ) >> pelley: no one died in the chlorine attack, b g shut down the hospital for a time. now, more is underground hospitals are being built by the syrian-american medical society. in the countryside, they're excavating a cave to replace a regional hospital that serves more than 200,000 people. the operating rooms are where? >> the main two... >> pelley: these two? >> yeah. >> pelley: the cave was already here. the limestone had eroded away over thousands of years. then the engineers came in. they