Diving just doesn't get any easier than this, although you'll be frustrated by the rules imposed by the management. Get geared-up on the beach-wide concrete landing, and walk the 10 meters over the black pebble beach to the water. There's no current, no large rocks, & no waves, so just walk out into chest-high water to don your fins & duck under water to start diving. Depths will slowly drop to 45' (13 meters). To the left (West), there's a small wall. Straight ahead, there's a sandy flat bottom. To the right (East), there's an interesting series of large stones and deep crevasses. If you continue to the right far enough, you'll find a very small cave along the shoreline. Visibility in August is about 10m (33 ft). Empty abalone shells litter the bottom. Omnipresent foot-high water plants mar visibility. No large fish inhabit the area, but expect frequent lionfish & goatfish. In August, waters are warm enough to dive in T-shirt & shorts. Some hardy (foolish ?) souls dive there in dry suits, year-round. Management provides every facility imaginable, but is quite strict, and may demand that you pay a dive guide to accompany you. This is a thinly veiled way for the management to get a few thousand yen & insurance coverage, each time you dive. This policy can quickly drive costs quite high. A paid dive guide with 2 tanks and weight belt for you, in this area, costs roughly 8,500 yen ($80 us dollars). Without the dive guide, a single full tank rents for 3,000 yen ($28 or so) from any dive shop in the region. Ouch. Renting a spot to put a tent, however, is only 500 yen per night, far FAR cheaper than any other accommodation in the region except for sleeping in your car. Nearby supermarkets and convenience stores, in addition to all the management-provided facilities, make this site's facilities outstanding. I was tempted, however, to search the surrounding island for suitable dive sites with no rules, no management, and no facilities, and found several interesting places along the road. Try a few spots further east along the south part of Omijima, or check out the shallow, clear water in a nearby beach-park on the southwest side of the island that connects Omijima to the mainland. (Look for a Poplar convenience store, and head West to the far shore then head a few hundred yards North to the beach park.) On the whole, you'll find this dive incredibly simple and safe.
Located on the north side of Yamaguchi, roughly 40 minutes' drive east from the Kyushu/Shimonoseki's bridge & 20 minutes' drive East from Hagi city. If you can read Kanji, it should be easy to find signs: Omijima's 3 kanji are the kanji for blue-ocean-island. The island has only one road, so you can't get lost ! Look for an aquiculture farm (a bay with fences across the mouth to keep fish inside) on the south-east side of the island. Across the street from this fish-farm, you'll see a pay-for-parking area with a single large 2-storey building. On the left side of the building, you'll see SCUBA tanks getting filled, and on the right side, you'll see a small restaurant. You can park here, or go back west 200 meters to a large free parking lot marked by a single soda machine. Park, unload, and walk behind the large building. You'll see a paved footpath leading past cabins, showers, an info-shelter, and a tent campground, to a small beach made of black round pebbles. That's the dive-site. You've actually walked 200 meters from the South shore to the North shore !