This door opens to the circular steps up to the illustrious Cavaillé-Coll organ (1877) of Notre-Dame-des-Champs. Yannick Merlin is co-titular organist here and is a substitute organist at Église Val-de-Grâce. Holly and I had the pleasure of listening to a rehearsal but could only see the top of the organist's head high above us in the organ loft.
As we prepared to exit the empty church this door opened and out walked M. Merlin himself. I did not lift my camera for a photo, but instead thanked him for the music.
You never know who you will run into in Paris.
92 bis, Boulevard du Montparnasse