The Tunnels of Gaza: How the subterranean maze below the Gaza Strip works.

"The Gaza Strip has all the harrowing pitfalls soldiers have learned to expect from urban warfare: high-rise ambushes, truncated lines of sight and, everywhere, vulnerable civilians with nowhere to hide. But as Israeli ground forces inch their way forward in Gaza, the bigger danger may prove to be underfoot. The Hamas militants who launched a bloody attack on Israel last month have built a maze of hidden tunnels some believe extend across most if not all of Gaza, the territory they control. And they are not mere tunnels. Snaking beneath dense residential areas, the passageways allow fighters to move around free from the eye of the enemy. There are also bunkers for stockpiling weapons, food and water, and even command centers and tunnels wide enough for vehicles, researchers believe. ..." 

NY Times