Had quite peculiar guests
The Sens hotel now houses the Forney Library of Fine Arts, but in the past it had quite peculiar guests such as Cardinal Pellevé (who died in a fit of rage when he learned that the Protestant Henry IV had entered Paris) and the libertine Margaret of Valois (ex-wife of the same king who beheaded an old lover because he had killed her favorite lover). Besides these fun stories, it's best building, it was recently restored and is one of the few preserved medieval buildings in Paris. To get there take the metro to Pont-Marie station. Closed on holidays.