You don't need to be religious to appreciate the serene atmosphere of Frejus Cathedral. Inquire when the next mass starts or when you can go for a wander through.
There's an admission fee to visit this principal church, which is located in Frejus City Centre. But there's loads more to see around these parts than just Frejus Cathedral. Frejus Amphitheatre, Frejus Beach and Saint-Raphael Beach are also worth adding to your itinerary.