Zenisu is a remote offshore reef group in the Izu Seven Islands, reachable only by charter boat from places such as Jinzu, Shimoda or Nishi-Izu. The site is an open-ocean drift dive with free descent and free ascent, so it suits experienced divers who want a big-water day rather than an easy local reef. It is best known for dense fish schools and pelagic action, with sharks, green turtles and occasional whales part of the draw.