Pakistan. Terrorists release a bio-weapon that winds up mutating. It's then a three front war, with the armed forces not understanding what these things are, and also not knowing that it requires headshots to take them out. As they finally come around, it may be too late, as they are in a race against time to stop the outbreak before it crosses the border into India...
A mine's a good one. Anywhere underground is often nice and creepy.
I've often wondered about the London Underground. Possibly the streets of London are overrun and people head into the Underground for shelter. Communities are set up in the old abandoned stations deep under the city. Someone gets lost in the deep dark tunnels with a couple of million zombies milling about. Cold. Dark. Alone. Trying desperately to find his / her way back / to camp.