Koya-san is the home of Shingon Buddhism within Japan. Kobo Daishi founded a monastery here in the 9th century and the sect is still going strong with a vast number of temples now forming a small town. The trip to Koya-san itself is interesting as the mountain slope is so steep that you have to transfer to a cable car for the final 500-meter ascent.
But Mount Koya is also a great place to experience something unique and different: an overnight stay at temple lodging. Many of the small temples here offer overnight accommodation and meals at a price and quality similar to a traditional Ryokan. During your stay, you can explore Buddhist philosophy.
I had a small tatami-mat room to myself with a kotatsu (heated table) with a view out to a lovely garden. There were many books about Buddhism that you could borrow to read more about beliefs in this quiet sanctuary.
At dinner, I was taken to a small private room with painted screens where I had a Buddhist vegetarian meal or 'shojin-ryori'. This meal has no meat, dairy or eggs, spices, onions, or garlic. The cuisine uses only uses fruit, tofu and leaves which can be taken without killing the entire plant that it came from. Think "food made by groovy people only using food that agreed to be in the dish in the first place". I had some tempura, miso soup, a vinegary salad, some pickles, a bean dish, a selection of steamed vegetables, and a hot pot with glass noodles, tofu, and mushrooms. For dessert, there was some opaque green jelly, with some orange curd and candied peel and strawberries.
This was tasty; as a carnivore I expected this meal to be bland or unsatisfying but it was delicious and full of rich flavors.
The temple also has a 'sento' shared bath which was great to relax in and soothe achy feet after a day exploring the sites of Koya. If this doesn't do the trick there is even a "foot massage path". It's a path of smooth pebble cobbles that you can walk on barefoot to relieve pressure points on the soles of the feet.
In the morning it is possible to join the monks for their prayers and meditation and learn more about the spirituality of Koya-san first hand.
You can book your overnight stay at one of the temples with the Koya-San Tourist Association.
The morning goma-taki was attended by only a handful of guests and residents. It was a deeply moving experience.