Fascinatingly means “in a way that is extremely interesting” — so interesting that people lean in and want to hear the next bit. You meet it in two places. One is beside a verb: a guide who talks fascinatingly about a tiny bird can hold a tired class. The other, and this is the one writers love, sits at the front of a whole sentence as a little comment from the speaker: “Fascinatingly, the same fish came back to that river every spring.” There it does not describe how someone moved; it flags a fact as gripping. It is a slightly bookish adverb, more at home in articles, documentaries, and careful talk than in the playground. People also stretch it: “fascinatingly enough” is often only “here is a mildly surprising bit,” not something that truly holds you. That is loose, but you will hear it.