It was supposed to be just a scouting mission. Basic archeology. The ruins looked to have been abandoned for ages, so you didn't even bring heavy weapons. But as you made camp that night, it was clear that something was watching you. Everyone in the group could feel it. None of you quite remember how the attack begun or quite what it was. Those who fought, died. You're sure of it. You ran. By some fluke of fate, many of you ran the same direction. It didn't matter which direction, so long as it was away. Panic and instinct guided you. They were not good guides. You woke up to the sun shining down on you from the collapsed ceiling, luckily having escaped the fall with just a few scrapes and bruises. But there was no way you were leaving the way you came. And you needed to leave. Preferably before sundown, when it would come to find you...

The group wakes up to the sun shining overhead through the hole they fell through. Save for a few scrapes and bruises (1 damage worth), they're okay. But the only way is forward.