When viewed from East Izu, Oshima Island is the mysterious gem floating on the horizon off in the distance to the right of Hatsushima. This pristine diving Mecca can be reached by ferry from Tokyo in less than 2 hours, and from Atami in 60 minutes.
Being farther out in the ocean, the water surrounding Oshima features superior visibility and a number of pristine shore-entry dive sites that offer excellent variety to all levels divers. Mild currents at some sites allow divers the feel of a short drift dive.
The fish and other marine life on Oshima are generally encountered in greater numbers and in larger sizes, compared to many mainland Izu dive locations. It’s a fantastic site and a rather well-kept secret, relative to other Izu sites. The easy access from Tokyo makes it an ideal getaway.
Oshima Island hosts a number of quaint minshuku and local shopping that make a weekend stay quite enjoyable.
Hachijojima is without a doubt my favorite diving destination we visit; visibility can approach 40 meters, temps are warm and turtles abound. It's paradise. The island is tropical above and below the water. Dives can find all kinds of marine life not found (or rarely found) in our home area.
We only go there once or twice a year due to its distance, and always choose a 3-day weekend for the event, usually in September and October. Due to the island location far to the south, we unfortunately have a high cancellation rate due to typhoons.
Shikinejima is just a bit north of Hachijojima, so it shares some of the same marine life. Lots of turtles. Due to a great deal of geothermal activity, there are a lot of natural onsen and Rotemburo, sometimes near to the dive sites. The trademark dive is a bay with natural onsen activity bubbling up from the bottom.
The beaches are fantastic. My personal opinion is that the beaches are actually better than the diving, but others disagree.