If you’ve been to Naoshima before, chances are that you have seen this Torii. It is located on the Benesse Art Site Beach in between Tsutsuji-so (the Mongolian yurt campground) and the famous Yellow Pumpkin.
It is pretty small (no more than two meters high) although I suspect that it is partly buried in the sand. I don’t really know anything about it (what shrine does it belong to? no idea, there doesn’t seem to be one in the vicinity), except for the fact that tourists like it (and it’s very easy to land a stone on it as you can see).