Israeli soldiers were stunned when they found the Hamas tunnel leading from Gaza toward an Israeli kibbutz. They knew that Palestinian militants had been digging tunnels for years, but they didn't expect anything so elaborate. The tunnel's walls, floors, and ceiling were made of concrete, and the tunnel was wired for electricity and communication. It was wide enough and tall enough to move quickly; a person could run with weapons, or even ride a motorcycle. 

"This tunnel is perfectly safe to be inside, which means that it is a very good building procedure," Israel Defense Forces Capt. Daniel Elbo says. And he would know -- Israeli military engineers briefed him after they checked it out. During the 2014 Gaza war, Hamas militants launched surprise attacks from tunnels that crossed under Israel's security fence and into Israel.