Mount Koyasan is a magical place, high in the mountains about 2 hours by train from Osaka. It is the “headquarters” of Shinto Buddhism, which gives it a very peaceful atmosphere.
You can sleep in a local temple and enjoy a vegetarian meal, see the photo for a feel of how many different dishes.
Tip: after dinner take a walk through town, even more serene and in my opinion an unforgettable experience.