As no-one has posted any more site descriptions in this thread for a while I thought that I'd add a bit about diving one of the islands in the Okinawa chain - Miyako-jima.
To get to Miyako you normally have to fly to Naha on the main island and take an 'island hopper' for another flight of about 50 minutes. Personally Miyako is my favorite place in Japan!
The main attraction for divers in Miyako are the caverns of Shimoji. Shimoji is a smaller island just off the coast - normally about an hour by boat from Miyako. The best caverns are normally dived only in the spring - up until the end of April - due to their location on the windward side of Shimoji.
These dives are not for beginners - several are quite deep. They are spectacular though.
Nakanoshima Channel.
This is often used as a warm up dive and to give the DM's a chance to check the capabilities of the divers before they take them into the main caverns. It's a dive to about 20 meters and around a maze of volcanic channels, tubes and small swim throughs. There are a lot of fish here - as well as quite a few banded sea snakes. There is very little coral due to the often very rough weather conditions - but the rock formations are simply beautiful and there is a lot to explore.
Nakanoshima Hole.
After the DM's have decided that everyone can handle themselves the next dive is often this. Dropping to the rock floor at 6 - 8 meters a short swim brings you to a small hole in the rock. You enter the hole one at a time feet first (you have to stay vertical as it's very tight). From there it's a drop down the chimney to a small cavern at 28 meters (this is NOT a dive for anyone suffering from claustraphobia!) The cavern exits back out into open water. The rest of the dive is slowly making your way back up the wall exploring as you go.
And now the three big ones!!
Antonio Gaudi.
With the main entrance at 36 meters this is an amazing dive. Once inside the cavern as you look up you can see tiny holes like windows all over the ceiling. The cavern is quite long and as you swim through it you ascend to the top exit at about 17 meters. On a sunny day the light coming through the holes is very beautiful. There are often small shoals of fish inside the cavern.
The Palace of Saturn.
In some ways this is quite similar to Antonio Gaudi. The entrance is at about 27 meters. The main attraction of this dive is the size of the cavern - it's huge. Again the ceiling has several small holes and windows letting in light. There are many wide passageways to explore giving a dive profile ranging from 25 - 15 meters and back two or three times. You have to watch your computer carefully on this dive as it's very easy to incur as small deco obligation - especially if it is the second dive after Antonio Gaudi. The DM's take you out and you hang around under the boat at 4-5 meters for about 15 minutes. My Suunto Vyper didn't like this dive very much!!! I thought it was great.
Torike.
If you see an aerial picture of Torike it's a small lake just inside the island:
In this picture the open sea is in front of you behind the ridge line. It's a small freshwater lake connected to the sea by a passage underwater. The roof of the passage is at 26 meters - the floor is about 43 meters. Basically the dive is from the sea - through the passage into the lake surfacing in the lake for about 10 minutes. It's not unusual to have very surprised tourists gawping at you from the path you can see in the picture! The DM's check everyones air and as long as everyone has 120 bar left you go back down and exit through the passage again. The passage is about 75 meters long. If you don't have enough air then you have to exit the lake and walk back to the sea to get back to the boat!! Apparantly it does happen sometimes - so this isn't a dive for a hoover!! Where the freshwater interfaces with the seawater the visibility virtually disappears generally through 5 to 10 meters of water.
These are the main dives at Shimoji - although there are a few more that I haven't done yet. If the weather isn't good enough to dive this side of the island then you have to go to the leeward side. There are several smaller sites there - again, lots of rock formations, small swimthroughs and caverns - including one cave called
Snake Hole which is a cave inside the mountain only accessable from underwater. You can surface inside the cave, but you need lights to see anything as it's completely dark inside.
If you like rocks and caverns then Miyako-jima is an amazing diving destination. It's also possible to take some very beautiful photo's there. Unfortunately when I went I didn't own a camera yet so I can't post any pics for you to see.