MUST-SEE: Benjamin Hall Takes an Exclusive Look Inside ISIS' Secret Tunnels
Iraqi and Kurdish forces are pushing into towns near Mosul, Iraq, as Defense Secretary Ash Carter makes an unannounced stop in the war-torn country.
In recent weeks, ISIS has been pushed out of areas it once held, revealing a network of tunnels.
Fox News' Benjamin Hall got an exclusive look at ISIS' clandestine tunnel system, which ran under every city and town the terror group held.
Recently, ISIS set fire to a sulfur plant, causing noxious fumes to float across the landscape.
But, the terrorists would have been safe in their tunnels, dug deep underground, Hall said.
Hall showed how the tunnels have many modern conveniences, including lighting, food, water and other comforts.
The tunnels are cut about 25 feet straight down into the bedrock, and then run laterally throughout the towns.
Hall said he and his team were the first journalists allowed inside the tunnels since they were recaptured by Kurdish forces.
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