I was searching for some wildlife hotspots in Japan and came across these images of Nomura's jellyfish (via Pinktentacle). The photos were taken just 5m underwater.

These jelly fish seem to invade the Sea of Japan each Autumn. According to wikipedia, and some divers who saw the jellyfish, these monsters can grow larger than a man, and they're known to have killed people with their stings. Not something I'd like to experience firsthand.