The monastery itself has a beautiful exterior, and the inside is incredibly ornate. I was the first one there around 8am and was surprised it was open. No one else was there, and it was a very nice experience. It's a bit dark on the inside, and no pictures are allowed, but it is still quite beautiful.
My favorite part was actually the gardens. When you walk in toward the back left, there are magnificent vistas that present great photo ops. The adjoining cemetery is also quite decadent, with every person having his or her own mausoleum in lieu of a traditional headstone. Make sure to check out Henri Matisse's grave while you're there!
That being said, it is a bit out of the way. If you're already venturing into Cimiez to check out the Matisse museum then it's no extra effort, but otherwise it may not be worth exploring if you are on a tight schedule. I intended to visit the monastery's museum also, but unfortunately it is closed from the 8th to the 25th of August 2022. Bummer.
Still, for an extra hour (not counting transportation), you can visit the monastery, see the museum, take a stroll in the gardens, and check out the cemetery that is home to Henri Matisse. Definitely worth it if you aren't otherwise engaged!
Happily,
Clayton Cohn