We had to meet 14-year-old Said in the dead of night, no camera lights allowed. We were just a few yards from the Egyptian border, with Gaza with its spotlights and heavily armed guards.
We walked in silence. Said and his two friends carried sacks on their backs containing their digging tools.
We crawled into the remains of a bombed-out building, feeling our way with our hands. Once inside, the teenage boys told us we could turn on our lights.
Said led us down deeper into the rubble, and then we were on our hands and knees. I have never liked confined spaces, and this was testing my resolve.
We arrived at the tunnel's opening -- a circular shaft reinforced by breeze blocks.
Said quickly jumped down and then, twisting his body, crawled backward into the smuggling tunnel until he disappeared, clouds of dust rising up towards us.
Despite his youth Said is an experienced tunnel digger. This is his fifth.
Since June when Hamas took control of Gaza by force, Israel has imposed a strict blockade on all but the most basic supplies. That has meant a boom in smuggling under the border with Egypt. The smuggling tunnels are working full time.
Said does it for the money. The smuggling bosses will pay him almost $7,000 when this tunnel is finished.
It will be used to smuggle everything from cigarettes and medicine to guns and bullets. They use him because he's small and brave.
The $7,000 is big money these days in Gaza, with its 70 percent unemployment. It is money Said uses to support his family.
When we were in Gaza we were told that anything can be smuggled.
You approach a smuggling gang, usually through an intermediary, and tell them what you want. It could be medication for your father, a computer game for your child or a new Kalashnikov rifle.
Several days later, the intermediary comes back with a price quote.
But working in the tunnels is hard and dangerous.
Said and his friends work all night, by hand.
Each tunnel takes months to dig. Said told me you need a hard heart to dig in the tunnels.
The conditions are cramped and airless. The dust is choking.
The boys pick at the roof of the tunnel with small spades and the blade of a pickax.
Large stones and bags of sand are passed out by hand. Nothing holds up the roof.
In the last two months several tunnels have collapsed.
While we were in Gaza, we ran into the funeral of a digger whose tunnel collapsed. It took four days to find the body.
Said does go to school, but only sometimes. His headmaster told us he despaired at what Said does but he understands the need to earn money for his family.
While we filmed Said in class it was clear his heart wasn't in it. Halfway through he got up and walked out, ready for another shift underground in his tunnel.
He told us he knew the dangers. He knew that one day his tunnel might turn into his grave.