Abandoned "Haunted" Summer Camp 
Young Adults, [s]couples trip?[/s], post-graduation (college) friend reuinon catch-up gone horror.
Meteor/Artifact/Relic/OOPart?
Superpowers ensue?
Kaiju monster forest creatures?
Lake Zombies, Zombie kids who drowned?
Different Wave Spectrum makes monsters invisible to normal humans, our heroes on the other hand, can see things no one else can due to an unhealthy dose of radiation.