Unable to answer "Do you need to pay to enter here?" for https://osm.org/node/1392914253 via StreetComplete 52.1:

The museum seems to be closed and merged with the Musee Sainte Croix in Poitiers.
https://fr.wikipedia.org/wiki/Mus%C3%A9e_Rupert-de-Chi%C3%A8vres