i mean, these four tunnels here, about -- >> matthew o'brien has agreed to lead us through a la brint of tunnels here that stretch for miles. >> goes under new york, new york and goes two miles total to the hard rock and opens up at that point. >> so there's a whole world essentially existing beneath the las vegas strip. >> exactly. yeah. there's hundreds of people who live in these underworld flood channels. how you doing, man? >> people like iron. a tunnel regular who matt met while researching his book "beneath the neon" about people living in the tunnels. >> can we get a quick tour? >> sure. >> iron is going to show us his home in the tunnels. >> ain't much. right there. it's just about basically a blanket and just pillows right now, because everything i had got washed away. >> so this is where you live? >> yeah. i have a little wall. i wasn't expecting company. >> the tunnel may provide the homeless an escape from vegas' scorching heat, but they were originally built to protect the city from flash floods. >> they are separate from the sewage system, as you can see, and it smells