Not far from Senlis is the former Benedictine Abbaye de Chaalis. At one time an important spiritual retreat for certain French kings (hence "royal"), the Abbye fell into disrepair after the Revolution and the confiscation of monastic lands. The Chapelle Sainte-Marie, however, has been preserved (and superbly restored). In a sense, this is a boutique chapel, possibly seating 30 comfortably, 45 in a pinch.
Built from 1250-55, its tall stained glass windows recall the use of light in the rayonnant stile in La Sainte Chapelle (Paris, completed in 1248), though no flying buttresses are required because the height is not extreme. The inner peace of the chapel is wonderful. This was to be used for the private offices of the Abbot (there were 8 offices in a 24-hour day). I was privileged to be in the chapel by myself for 20 minutes, about the length of a shorter daytime office, before other visitors entered. I could imagine myself being the Abbot (without any responsibilities of course) and I also enjoyed singing a few Gregorian chants and intoning parts of several Psalms by memory in the wonderful acoustical space.