He looked at the sky once more. Men had gone out there, he thought in wonder, and couldn't think why. Singly and in small groups they had gone into strange lands, across wide seas, had climbed mountains where no human foot had ever trod. And he couldn't think why they had done these things. What impulse had driven them from their own kind to perish alone, or among strangers.
Kate Wilhelm, Where Late the Sweet Birds Sang
apocalypse, doomsday