entrance fee unfortunately.
Wikipedia summary: Royaumont Abbey is a former Cistercian monastery located in the hamlet of Baillon in Asnières-sur-Oise in the Val-d'Oise, about thirty kilometers north of Paris.
It was built between 1228 and 1235 under the aegis of Saint Louis, and was then one of the most important abbeys in France. It remains a Cistercian abbey until the French Revolution, it is sold as national property and becomes a textile industrial site. It regained its religious vocation in 1864, until the Combes laws in 1905. The abbey was then bought by Jules Goüin, and his grandson Henry, an industrialist and music lover, opened its doors to artists, organized concerts there and makes a place of musical and cultural creation. He gave it to the Royaumont Foundation, which he created in 1964, the first private foundation for cultural purposes, which has since managed the site.
The building has been listed as a historical monument since 1927 for its remains, and 1948 for the buildings of the abbey and the park.