We had booked a morning visit to Saihō-ji, a zen temple famous for its moss-covered gardens, and having arrived rather early so we could take a walk around the mountain setting, we discovered what is the southernmost end of the Arashiyama park. Most people enter at the Monkey Park or Tenryu-ji, and from a distance on the highway you can see the throngs of people lining up for a visit to either.
We ourselves had planned to also enter from there on the following day, but we count ourselves very fortunate to find that Arashima Mountain had the southern entry point. The area of the entrance is residential, and we just followed a few early morning elderly hikers along the mountain path. We didn't realize where we were until we saw a map of the mountain paths.
The serenity of the area, lack of tourists, the beauty of both the bamboo and other trees enclosing us, all of this put us into the perfect mindset for our later visit to Saiho-ji. We spent about an hour and half just wandering around the mountain paths, only encountering a handful of people. No crowds, no annoying self-proclaimed "influencers" taking selfies or filming video -- just natural beauty and peace.
If you planned for a full morning or afternoon, you could eventually walk the 4+ kilometers to the northern exit and eventually meet up with the tourist crowds. but that kind of defeats the purpose of such an excursion in our opinion.
At the entrance gate there was a sign warning to watch out for bears. We didn't see any. It was just us, the trees, the bamboo, and the sounds of birds and flowing water from the various streams.