cnn's casey wayian and his cameraman went inside to give you an up-close look. >> this is the way angents first discovered this tunnel a few days ago, under this giant container of water. over here, you can still see 55 gallon drums that contain the dirt that was dug out of this tunnel stretching 240 yards across the u.s./mexico border. >> this is the most vice cane one i've ever seen in arizona. >> why is that? >> most tunnels we have under arizona, those are just digging through dirt to get into the sewer system. using the sewer system and punching out again. this one, when you look down that hole, you see it is completely four by six all the way, play wood all the way around it. rebar in there reinforced. >> the tunnel is so narrow and so deep, cnn foet why journalist and his camera needed to descend separately. >> clear the shaft. >> clear the shaft! >> okay. >> each with the help after harness. >> it gets even smaller? ? >> it gets smaller toward mexico. we actually have to crawl to get much further. >> there is absolutely in dirt in here. it is very clean. and there is light. there

cnn's casey wayian and his cameraman went inside to give you an up-close look. >> this is the way angentsvered this tunnel a few days ago, under this giant container of water. over here, you can still see 55 gallon drums that contain the dirt that was dug out of this tunnel stretching 240 yards across the u.s./mexico border. >> this is the most vice cane one i've ever seen in arizona. >> why is that? >> most tunnels we have under arizona, those are just digging through dirt to get into the sewer system. using the sewer system and punching out again. this one, when you look down that hole, you see it is completely four by six all the way, play wood all the way around it. rebar in there reinforced. >> the tunnel is so narrow and so deep, cnn foet why journalist and his camera needed to descend separately. >> clear the shaft. >> clear the shaft! >> okay. >> each with the help after harness. >> it gets even smaller? ? >> it gets smaller toward mexico. we actually have to crawl to get much further. >> there is absolutely in dirt in here. it is very clean. and there is light. there is electrici