An Israeli colonel likens the hunt for tunnels dug by Palestinian militants from the coastal enclave of Gaza to the work of a detective.
"Finding these tunnels is like a detective trying to solve a murder with a number of clues. There are several pieces to the puzzle, including intelligence and technology," said Lieutenant Colonel Max of the army engineers for the Gaza area.
Israel has said uncovering and destroying an apparently sophisticated network of tunnels is a primary goal of its assault unleashed on July 8 in Gaza, particularly its ground invasion.
For the first time, the army on Friday gave foreign media access to part of the network, including a tunnel running more than three kilometres (two miles) from southern Gaza's Khan Yunis to near the Israeli kibbutz of Nir-Am.
Max, who declined to give his family name, said the Israeli end of the tunnel was discovered two months ago.
But its entrance in Khan Yunis was uncovered this week during the Israeli ground operation launched on July 17.
The tunnel is 1.75 metres high (six foot) and over 70 centimetres across, with its sides reinforced by closely-fitted concrete blocks and ceiling inlaid with arched concrete plates.
"Big enough for a man in full body armour to go through standing up," said Max.
The Islamist movement group Hamas which controls Gaza "could have put through dozens, even hundreds of terrorists through this tunnel out on the Israeli side before we would have discovered it."
Max said 26,000 components were used in the construction of the tunnel, estimating it must have cost around one million dollars to build.
Along one wall is a rack to string electric cables, while a metal dual track runs on the floor, similar to inside a mine shaft.
Max said the track was used to remove earth during construction and could also have been designed to ferry equipment and arms into Israel.
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In part of the tunnel, a narrow niche has been carved out to store equipment and weapons.
- Booby traps -
The army is planning to completely destroy the tunnel within days using explosives, but the process is dangerous, Max said.
"You excavate through one of the tunnel walls and it can collapse," he said.
"Within the tunnel itself there can be booby traps, within and just around the entrance there can be booby traps, or there can be one of the enemy waiting within the tunnel.
"The biggest dangers though are not in the tunnels themselves but in the surrounding areas where we have to work, where you can have mines, anti-tank weapons, snipers, artillery."
So far, the army has found 30 tunnels, and over 100 shafts leading into them.
Max said the army tries to destroy the tunnels it finds from both ends, to ensure they cannot be reused in the future.
"You want to reach a point where the entire tunnel, from end to end, is destroyed, so the other side can't come back and use it another time," he said.
"Each tunnel takes a couple of days for us to deal with it."
Max said the soldiers needed about another week "if we want to neutralise all the tunnels ... at least all the tunnels that we know about."