Koyasan is reached from Osaka via the Nankai Koya Line from Namba station, a journey of about 80 minutes to Gokurakubashi at the mountain's base. From there, a five-minute cable car (Koyasan Roper Railway) ascends to the plateau. The total journey from central Osaka takes around two hours. The Koyasan World Heritage Ticket, sold at Nankai stations, covers the train, cable car, and bus travel on the mountain, and is worth buying even for a day trip. The route is not covered by the JR Pass.
From Kyoto, the most convenient approach is by limited express via Osaka Namba. Allow about three hours total. Day-tripping from Tokyo is possible but leaves little time on the mountain — an overnight stay is far preferable.