User blog comment:SPARTAN 119/Nobody Survives Forever: A Survival Battle Royale/@comment-379205-20190326092019/@comment-422690-20190326144351

I'd personally go a step farther than Hashima. Have the sea around it a dead zone, whether by algal bloom, natural causes, or meta magic. Essentially, remove *any* secondary method of survival. If you want to keep the predators, have a pack of wolves escaped from a ruined zoo; this will create not only a physical hazard but also a starvation hazard, as they'll be searching for the caches, too. This will add a secondary food method, but one that's highly limited and won't affect the possible conflicts.