Literally anywhere there is water! If you are staying in the Yomitan area there is a big beach that you can walk too that has great snorkeling. A short drive away is Blue Cave which is a tourist attraction for snorkeling as well.
Coral farm
You can do your own glass blowing here! Costs about $20 and you can pick your glass shape, colors and texture
Around $170 for jigging/drifting/tolling Comes with bate and poles to achieve the above, they also fillet the fish for you and you take it home!
Also great prices as the other company listed