There was a movie where the US selected a dozen people to "survive" the end of the world and re-populate the earth. These people woke up in a facility far underground and were to live there until it was safe to come out. As luck would have it, lab animals and eventually the people themselves were being killed by bats. They realize it is just an "experiment" to see if people really could survive and repopulate, so they decide to try and climb up the elevator shaft to the surface. Part way up the shaft they find a breach in the shaft wall opening into a cavern filled with carnivorus bats.
