well don’t be mistaken, Paris is not a very beautiful town actually lots of urban legends and myths and lots of history and museums and good tourism but that’s not what I’d call “beautiful”
About gaming shops I am not sure about which one still sell mithril or not but some of the oldest RPG shops are near the university at Jussieu, one of the most famous names is “l’Oeuf Cube” (it used to be, and still is, a great place for Magic the Gathering CCG trading and selling, old RPG books and lots of figurines but I don’t think they still have mithril…
If you continue on the big avenue leading from Jussieu to St-Michel quarter, you’ll find Descartes shops too. that sometimes have rarities, but lately not as much as they used to have
as for museums and things to visits, indeed there are tons… le Louvre, la Tour Eiffel, Middle-Age museum, the Champs-Elysees…