fascini

The root is fascin-, one piece, and that needs saying because the letters -in- sitting in the middle of it look exactly like the feminine suffix. They are not. Fascini has nothing to do with -in-, there is no masculine *fasco for it to be derived from, and the word divides only into fascin- plus the verb ending. The same trap catches kuzino and magazino, where the -in- is also just part of the borrowed spelling, and it is worth learning to check whether removing the suffix leaves a real word behind. Here it does not.

Meaning-wise, fascini is the strong end of the interest scale. Something merely interesting is interesa; something that holds you against your will is fascina. Ravi is close but warmer, more delighted than transfixed, and sorĉi is the literal bewitching that fascini used to mean and no longer does.

Note the case pattern in the third example. Min fascinas la lingvoj puts the thing doing the fascinating in the subject slot and the person in the accusative, which is the natural Esperanto order for this verb and the reverse of the English one. Mi fascinas la lingvojn would mean you are casting the spell on the languages.