As a day trip from Nara I visited Yoshino to see the Kii Mountains. From the valley where the train station is located I took a cable car up the hill. I arrived in a tourist village with plenty of shops and restaurants. The village also contains Kinpusen-ji, an important temple of the region.
From the village I set out to hike along the pilgrim path into the Kii Mountains. On my way I crossed multiple temples and everything quieted down; there were not that many hikers, but that may have been caused by me visiting outside vacation season.
Along the trail I passed several temples, e.g. Kinpu Shrine shown in the picture. However, the scenery wasn't great as this is still a fairly civilized area. Some parts were even open to logging activities. Personally, I would have liked to venture further into the mountain range, probably with an overnight. My expectation would be that the more remote parts should offer a better experience. Still, I had a nice time.
Arriving in autumn I did miss on the most famous feature of Yoshino, though. The Japanese believe Mount Yoshinoyama to be Japan's best cherry blossom viewing spot.
Getting There
There are several access points to the Kii Mountains. From Nara you can go to Yoshino by direct train. Be aware that the train line is private and not included in the Japan Rail pass. Along the way you will pass the tentative site of Asuka-Fujiwara.
From Osaka Koyasan seems the easier option. It takes 90min by train.
In Yoshino and Koyasan you will find a cable car to take you up the mountains.