The Louvre may seem like an obvious and somewhat touristic choice in Paris- but it is truly one of the most exquisite museums in the world.

Reserve tickets online beforehand and arrive early- and still expect to queue. See the Mona Lisa for the sake of seeing her. But the real attraction, in my opinion, is the Richelieu wing and the apartments of Napoleon III.

This museum is also free  for EU residents aged 25 and under, with ID. I recommend to go alone and put some Tchaikovsky in your headphoness for a refined museum experience.