You needn't be of strong faith to enjoy the serene atmosphere of Alexander Nevsky Cathedral. Check when the next mass is scheduled or when you can go for a wander through.
This 8th Arrondissement principal church is a good place to begin your day of sightseeing. There's loads to do and see in the area, like Eiffel Tower, Louvre Museum, and Arc de Triomphe. Take your time at Alexander Nevsky Cathedral before making tracks to these other fine sights.