From Kyodo via Japan Today
KAGOSHIMA — Police said Sunday that four 13-year-old boys who died of carbon monoxide poisoning from a bonfire they made in a cave on Saturday in the city of Kagoshima had air guns and knives with them, and may have been playing an adventure game inside the cave, believed to be an old air raid shelter
Caves in Japan don't seem like a wonderfully safe place to be. What are you likely to find in them? Unexploded decaying WWII ordinance, yakuza victims bodies to add to the normal caving hazards.
