Part of an on-going series highlighting some of my recommendations for travel in Japan.
Perhaps my favourite destination in Japan, Kōya-san (Mt. Kōya) is situated to the east of Wakayama Prefecture, south of Osaka. It is the centre of Shingon Buddhism, and the perfect place to pause for a little while. I recommend staying in one of the many templates and, if you rise early enough, attending morning ceremonies.
The train journey from Tokyo to Koya-san is a leisurely one on local trains, winding, over the course of many hours, through Nara Prefecture, ending with a cable car up the mountain itself.