If you want a memorable experience in Japan which you will never forget, you have to go to Koyasan.
Via Japaneseguesthouses you can book a stay at one of the temples at Koyasan which are managed by monks. You can experience the culture and way of living of the monks up close.
The meals (dinner and breakfast) which are included are of excellent quality. When you stay you are requested to attent a morning ceremony in the temple where you can experience 40 minutes of chanting and prayer.
There is an important graveyard with millions is graves in a cedar wood wood, which will certainly move you. Even the ride by train to Koyasan with a mountain train and cablecar to the tranquil village makes the trip worth it, also make a walk at nigth when the village is almost deserted.