Koyasan, Mt.Koya is a headquarter of Shingon sect of esoteric buddhism. You can enjoy this holy place started by the great priest, Kobodaishi Kukai.
Kumanokodo is a pilgrimage site visited by emperors, mountain priests, common people etc. from the ancient time. Japanese people have bilieved that gods reside in nature.
Both are registered as UNESCO World Heritage Site.
Airport/Sta.Tokyo International Airport (about 414km) Google Transit