Daigo-ji Temple.

Overview: Daigo-ji Temple is the headquarters of the Daigo branch of the Shingon mission. It was built by a Buddhist monk, named Shobo Rigen Daishi, in 874.
Daigo-ji temple is situated at Mt Kasatori (Mt Daigo), and the complex covers the mountain from top-to-bottom. The area, on the top of the mountain, is commonly known as Kami-Daigo (the upper part of Daigo), while the expanse, at the foot of the mountain, is called Shimo-Daigo (the lower part of Daigo).
With more than 1,000-years of history, Daigo-ji temple has retained an important position in the history of Buddhism in Japan. Many of it's artifacts, protected for a long period of time, have been designated as "National Treasures" and "Important Cultural Assets". In 1994, Daigo-ji temple was registered as a "World Cultural Heritage Site" by U.N.E.S.C.O.
Many annual events, having a long history and tradition, are still held, including, in particular, the "Godai-Rikison Minno-e Festival", held each February. This is a contest where participants compete to see who can lift and hold huge amounts of Mochi (steam pounded rice). On the night of August 5th, Daigo-ji temple is surrounded by the lights of candles and paper-lanterns, which bless all life."Cherry Blossom" season (April/May) is also a popular time to be visiting Daigo-ji temple.

Tips: Daigo-ji is open from 9am-to-5pm March to December, and 9am-to-4pm December to February.
Any-time of the year, is a good time of year to visit Daigo-ji. But, if you can time your visit for one of the many festivals (check the website)you can take-in the beauty and history as well as attending the festival.
Bring a picnic lunch, and plenty to drink,(there is a supermarket at Daigo subway station) especially if you plan to visit Kami-Daigo.It is quite a steep climb to the upper complex, taking about 1-hour. 30-minutes up, there is a rest-stop, providing shelter, seating and cold water to refresh before your final ascent. Believe me, the climb is well worth the effort.
Access; via Train - take the J.R.train to Yamashina station, change to the subway Tozai Line, to Daigo station. Or, take the Tozai Line from the Keihan Sanjo station.Once at Daigo station, exit from gate-2. From there it is a 15-minute walk to Daigo-ji. Check the website for further details (I have commenced and finished this hike from Daigo station).
Don't be in a hurry to view Daigo-ji temple, I suggest at least half-a-day will cover the entire complex, both upper-and-lower.