Where is the Preferences page?

I'm wondering because I might like the option to have underlined wikilinks. Maybe I don't. But I think it would be good to have the option. Similarly, we could then make the boxes bigger depending on what you wanted to put in. Because when I edit, I tend to have run-on lines, and I'd like to widen the box so it can be wider, to make it easier. But I cannot find the special:mypreferences, which I think has all of that sort of option on. Can a founder shed any light on this?